BIOLOGY

UERARY

G

HOME UNIVERSITY LIBRARY
OF MODERN KNOWLEDGE

THE

PRINCIPLES OF PHYSIOLOGY

BY

JOHN GRAY McKENDRICK

LONDON
WILLIAMS & NORGATE

HENRY HOLT & Co., NEW YORK
CANADA: WM. BRIGGS, TORONTO
INDIA : R. & T. WASHBOURNE, LTD.

1

WAI MB

m ROMF m

/»»

•\ -] rlvJMJi -FT

UNIVERSITY

LIBRARY

OF

MODERN KNOWLEDGE

Editors :

HERBERT FISHER, M.A, F.B.A.

PROF. GILBERT MURRAY, D.LITT-
LL.D., F.B.A.

PROF. J. ARTHUR THOMSON, M.A,

< Kb

p^=

PROF. WILLIAM T. BREWSTER, M.A,
(COLUMBIA UNIVERSITY, U.S.A.)

255= r ia

M r1—

NEW YORK

HENRY HOLT AND COMPANY

THE

PRINCIPLES OF
PHYSIOLOGY

BY

JOHN GRAY McKENDRICK

M.D., LL.D., K.R.S., F.Vc.r.E., M.R.I.

Emeritus-Profassor of Physiology,
University of Glasgow

B LONDON
WILLIAMS AND NORGATE

<

---, ,

^.

6

PRINTED BY

THE LONDON AND NORWICH PRESS, LIMITED
LONDON AND NORWICH

PREFACE

THIS is in no sense a Text Book. It is rather
an attempt to state the leading principles and
facts of physiology, and more especially of
human physiology, in such a way as will be
understood by an intelligent reader who has
had no special scientific training. If the
perusal of this little book leads the reader
to wish to know more of this fascinating
science, which, in a sense, is the meeting-point
of many sciences, he is referred to the Bib-
liography, and the aim of the writer will be
accomplished.

J. G. M.
MAXIEBURN,
STONEHAVEN,
January, 1912.

252437

CONTENTS

CHAPTER

I PHYSIOLOGY, ITS SCOPE, AIMS, AND

RELATION TO OTHER SCIENCES . 9

II THE CHARACTERISTICS OF LIVING OR-
GANISMS 20

III THE ACTIVITIES OF LIVING BEINGS. . 30

IV ORIGIN AND DEVELOPMENT OF THE

INDIVIDUAL ..... 37

V THE DEVELOPMENT OF TISSUES AND

ORGANS 55

VI MATTER AND ENERGY IN THE LIVING

BODY, CHEMICAL PROCESSES . . 65

VII INCOME OF MATTER, ABSORPTION OF

FOOD -STUFFS ..... 90

VIII THE BLOOD : ITS RELATION TO LIVING

TISSUES 109

IX THE OUTPUT OF WASTE MATTER . . 125

X HIDDEN PROCESSES AND ULTIMATE

PHENOMENA OF NUTRITION . . 144

XI THE LIBERATION OF ENERGY . . 161

XII THE REGULATING MECHANISM. NERVOUS

SYSTEM ... 69

8 CONTENTS

CHAPTER PAGE

XIII RELATION TO THE OUTER AND INNER

WORLDS BY THE SENSES . . 214

XIV THE VOICE 226

XV DEATH 235

XVI PHILOSOPHICAL REFLECTIONS. THE

TREND OF PHYSIOLOGY . . . 239

XVII BIBLIOGRAPHY 243

GLOSSARY 245

HISTORICAL NOTES .... 25?

INDEX .... 255

THE PRINCIPLES OF
PHYSIOLOGY

CHAPTER I

ITS SCOPE, AIMS AND RELATIONS

1. PHYSIOLOGY is the science which describes
and endeavours to explain the phenomena
manifested by living beings. It may also be
said to treat of the changes that occur in
living matter. It deals with that special
mode of activity we call Life.

2. Living beings are divided into plants
and animals. There are many forms difficult
to classify ; these seem to belong to either the
plant or the animal world, according to the
point of view from which we regard them.
All living things, however, show certain
general characters, by which we know they
are alive. They are developed from a parent

or parents, they require food and oxygen,
9

10 PRINCIPLES OF PHYSIOLOGY

they pass through a number of stages in their
existence, they reproduce their kind, and they
die. It may not always be easy to observe
some of these phenomena in the lower forms,
but we find that their bodies are composed of
matter that possesses certain properties, and
we characterize such matter as being alive.

3. One of the lessons of scientific investiga-
tion is that in the study of phenomena we find
transition — a series of changes, and the gradual
passage of one state into another — while a
superficial examination may appear to establish
clear lines of division between different depart-
ments of knowledge. Thus we distinguish
between that which we say is dead matter,
and that which we consider to be alive.
More careful examination, however, shows
that certain properties may be the same, or
similar, in both dead and living matter. Thus
a crystal, which we regard as dead, grows
and increases in size in accordance with
physical laws. Living matter also grows and
increases in size, but by a different process
from that of a crystal. So that mere increase
in size, in certain conditions, may characterize

SCOPE AND AIMS 11

both that which is dead and that which is
alive. Changes even in the minute structure
of both dead and living matter may occur.
For example, it is known that slow changes
may happen in the structure of even hard
metals. Particles of gold may penetrate
into a mass of solid lead, and solid bodies
may even, by slow movements, sink into an
apparently brittle mass of cobblers' wax.
Slow changes probably occur in all kinds of
matter, even the most dense and durable.
Thus molecular changes, or, in other words,
movements, may occur in matter which we
call dead. Molecular movements also occur
in living matter, so that such minute move-
ments do not enable us to distinguish between
what is dead and what is alive. Both dead
and living matter, again, are subject to the
laws of gravitation, and many electrical and
optical phenomena are manifested in a
similar way by so-called dead and by so-called
living matter.

4. There is no difficulty, however, in recog-
nizing many of the phenomena of life in one
of the higher forms, whether it be a plant

12 PRINCIPLES OF PHYSIOLOGY

or an animal. Thus one of the higher plants
is rooted to the soil, from which it mainly
derives nourishment ; it spreads its branches
and leaves and flowers to the air, and it
breathes. An animal of the higher orders
shows active movements such as running or
leaping, it breathes, it requires food, and it
can produce heat. We find accordingly that
there are phenomena to be observed and
explained in both the plant and the animal.
It is the province of the physiologist to study
those phenomena and to offer explanations.
The field of work, however, is so immense that
the science naturally subdivides into plant and
animal physiology. The first is a division of
the science of Botany, while that of the latter
falls into the domain of the Zoologist. Thus,
in a sense, all the phenomena of living things
fall into those two sciences, but, by common
consent, the task of describing and explaining
the phenomena on which life depends, is
relegated to physiology, and this again may be
subdivided into the physiologies of the various
animals. We discuss the phenomena occur-
ring in the body of man as Human Physiology,

SCOPE AND AIMS 13

but we might equally well discuss the physi-
ology of the domestic animals, such as that
of the horse or ox, or the physiology of birds,
or, indeed, of any group of animals. It is
found that no sufficient explanation of many
vital phenomena can be given by the study
of one animal, or group of animals, and
accordingly knowledge may be brought to a
focus in the department of science called
Comparative Physiology.

At one time the word physiology expressed
all that we now term physics (phusis, nature,
logos, a description), a description of natural
phenomena in general. For many years,
however, its meaning has been limited to the
discussion of phenomena as these occur in
living beings.

5. But all science is in a sense one, and
accordingly we find that the compartments of
knowledge we call the sciences are related to
each other. Physiology is closely related to,
and largely depends on, three sciences :
Anatomy, Physics and Chemistry. A general
acquaintance with these sciences is of para-
mount importance to any one about to enter

14 PRINCIPLES OF PHYSIOLOGY

on the study of physiology. One should know
something of the plan of structure met with
in the great subdivisions of the animal kingdom.
The student of human physiology, for exam-
ple, should be acquainted with the general
anatomy of the human body, and of its various
organs, although much may be learned from
the dissection of one of the lower mammals,
such as the rabbit. Not only is it necessary
to study the forms and relations to other
parts of the various organs, as seen by the
naked eye, but also the minute structure of the
organs and tissues as revealed by the micro-
scope, and by modern technical methods of
preparing these for examination. This is the
department known as Histology, a depart-
ment of science that in recent years has made
enormous progress. The demands of one
science stimulate another, and we find an
example in the development of the modern
microscope, which, both in its mechanical and
optical arrangements, may be regarded as a
nearly perfect scientific instrument. The
methods of hardening, cutting into thin
sections, and staining by various colouring

SCOPE AND AIMS 15

matters are now highly skilful and accurate.
Histology has both a morphological side, in
as far as it deals with form, and a physiological
when it treats of the functions performed by
these tissues. Further, much information is
furnished to the physiologist by the examina-
tion of the body at various stages of growth,
and more especially in the earlier stages.
Thus the study of the formation and early
development of the embryo, and tracing the
origin of the tissues, and the gradual building
up of the more complicated organs, have >
thrown light on vital phenomena. This line '
of research is known as Embryology.

The body is also the theatre of many
phenomena of a chemical character ; indeed
it may be said that the phenomena of life
depend essentially on chemical changes. As
we shall see, food and oxygen are introduced
into the body, and, by chemical changes,
often of a complicated kind, many chemical
substances are formed, some of which are built
into the tissues, while others are thrown out
as effete. Many of the operations in the
digestion of food and in the formation of

16 PRINCIPLES OF PHYSIOLOGY

substances in the blood are purely chemical.
Physiological Chemistry has as its field a
description of the physical and chemical char-
acter of the substances forming the tissues
and existing in the fluids of the body. It
also gives an explanation of the chemical
processes occurring in the body. This depart-
ment of science has also made great progress
in recent years. At one time it was thought
that certain substances formed in the body
could be formed only in living matter. The
synthesis of urea by Wohler in 1828 upset this
notion. This experiment laid the foundations
of organic chemistry. Since then hundreds of
chemical substances found in plant or animal
tissues have been formed synthetically by the
chemist by the operation of chemical methods.
It is remarkable, however, that in living matter
such substances are formed by molecular
action and by hidden processes, while the
chemist can only form them by the agency
of high temperatures, and the action of power-
ful substances such as acids or oxydising or
reducing substances. It is possible that the
processes of nature and of the chemist may in

SCOPE AND AIMS 17

essence be identical, or at all events similar,
but this is doubtful.

6. The laws of physics are applied by the
physiologist to the investigation of the
motions of the solids and fluids in the animal
organism. Thus the movements of the limbs
in locomotion are mechanical, the movements
of the blood in the circulation are subject to
the physical laws of hydrodynamics, the
interchanges of gases between the air and
the blood in respiration are to be explained
as special cases of the transfusion of gases
through thin membranes, while the actions
of the eye and ear can only be understood
by the study of optics and acoustics and
their application to these highly specialized
mechanisms. The absorption into the blood
of nutrient matters, after their preparation by
digestion, and the elimination of waste matters
from the blood by various organs, are so far
to be explained by the laws regulating the
passage of fluids through thin membranes,
and which are studied by the physicist.
It may indeed be said that physical processes
are more or less involved in all the phenomena
B

18 PRINCIPLES OF PHYSIOLOGY

of living matter. It would also seem that
electricity plays an important part in vital
activities, or, at all events, it is intimately
related to the intricate and hidden molecular
phenomena on which life depends. Finally,
the phenomena of the living being can only
be accounted for by their consideration in the
light of the modern doctrine of the conserva-
tion of energy, a doctrine which may be said
to have originated in the study of these
phenomena. The history of this great idea
shows that the endeavour to account for
animal heat and the relation of food and
oxygen to the production of heat and of
animal movements, was one of the first steps
towards the building up this doctrine, which
lies at the foundation of all physical, chemical
and biological science.

7. Thus, physiology rests on a tripod of
three sciences — Anatomy, Chemistry, and
Physics. It brings to bear on its problems
all the information that can be gathered from
those sciences, considered in their broadest
relations, and while physiology has its own
methods, it may be said to be the mechanical

SCOPE AND AIMS 10

and chemical interpretation of phenomena
happening in living matter. We shall see,
however, that in the present state of the
science there are not a few phenomena which
cannot be so explained. Such phenomena
are provisionally termed vital. Meantime
we may note that as physiological science
advances, vital phenomena are more and
more regarded as special examples of the
operation of chemical and physical laws.
Still there are at present, and it is not going
too far to assert that there must always be,
some phenomena that cannot be so explained.
Thus it would appear to be impossible ever to
account for feeling, willing, thinking, and other
mental (psychical) states or processes by any
purely physical or chemical operations.

CHAPTER II

THE CHARACTERISTICS OF LIVING ORGANISMS

CERTAIN of these have already been referred
to. We may now consider some of the
characteristics of living beings more fully.

8. Physical structure. No living matter
ever assumes a crystalline form, but crystals
may be imbedded in it. Living matter is
always soft, jelly-like, diffluent, readily per-
meated by water, oxygen, and the crystalloids.
It is matter in a colloidal state, which, as it
permits of the free play of molecular inter-
changes, has been termed a dynamical state
of matter. The colloidal shape is not, however,
peculiar to living matter, as it is shown by
certain conditions of silicic acid, peroxide of
iron, etc. The firmer portions of living matter
are always soft ; they readily absorb water
by imbibition. It has been supposed that
living matter consists of still more minute
20

LIVING ORGANISMS 21

particles, possibly of irregular form, and that
water fills up the spaces between such particles.
Such molecules are assumed to be in a state
of incessant movement, and these movements
are associated with the absorption and libera-
tion of water. A watery consistence is
essential to the phenomena of life. Move-
ments of minute particles of matter in a
fluid are well illustrated by the Brownian
movements seen under the microscope, magni-
fying say 250 diameters, if we squeeze and
examine a little bit of fresh vegetable tissue.
The minute particles are seen to be in a state
of incessant vibration.

9. Chemical composition. Of the seventy
elements known to chemists only from eighteen
to twenty have been found in living matter,
and of these the chief are oxygen, hydrogen,
nitrogen and carbon. With these are asso-
ciated, of the non-metals, sulphur, phosphorus,
and chlorine ; of the alkalies, sodium and
potassium; of the alkaline earths, calcium
and magnesium ; and of the metals only one,
iron. Minute quantities of other substances
have been found, such as argon, silicon,

22 PRINCIPLES OF PHYSIOLOGY

fluorine, iodine, bromine, manganese, and
copper, but the presence of some of these sub-
stances may be accidental. It should be noted
that carbon and nitrogen, along with hydrogen
and oxygen, are essential to life. Oxygen and
hydrogen are often in the proportions that form
water — 2 of hydrogen to 1 of oxygen. From
these elements complex chemical substances
are built up. Thus the living matter in the
cells of a plant, mainly under the stimulus
of light, so combines carbon, hydrogen and
oxygen as to form starches, sugars, and fats ;
and it may also form still more complex
chemical substances, known as proteins,
which contain carbon, hydrogen, and oxygen,
and the all important element nitrogen.
Such bodies, often termed proximate prin-
ciples, thus formed in a plant, may become
the food of an animal and be built into its
tissues, or be directly used up in various
transformations connected with vital activity.
The term proximate principle was given by
the earlier physiological chemists, because they
thought that certain substances, such as the
proteins (albumen, etc.) existed in the tissues

LIVING ORGANISMS 23

or fluids as they were known to the chemist.
We now know that this is an assumption.
These so-called principles probably only arise
from the decomposition of matter that was
once alive. One of the characteristics of
these complex organic substances, whether
as found in the bodies of plants or animals,
is their instability. They are liable to split
up into simpler bodies, and this splitting up
is always associated with the liberation of
energy, chiefly as heat or movement. Thus,
in living matter two apparently opposite
chemical processes are continually at work ;
there is either the building up of simpler
substances into more complex ones, such as the
formation of starch from the elements carbon,
hydrogen, and oxygen, or the pulling down of
complex substances into simpler ones, as the
resolution of starch into carbonic acid and
water. In the upbuilding process, often termed
anabolic, energy is locked up, or becomes
latent, while in the pulling down process,
termed katdbolic, energy is liberated and
becomes kinetic. Thus starch (or oil), when
burnt, that is oxidised, yields carbonic acid

24 PRINCIPLES OF PHYSIOLOGY

and water, and energy is liberated as heat,
which may be transformed into the motion
of a steam engine and caused to do work.
Living matter is thus continually undergoing
a series of chemical changes of composition
and decomposition, as a result of which there
is an incessant renovation of its particles.
It would appear that chemical changes are a
necessary condition of the action of living
matter ; part of the living matter dies, is
decomposed, or rather, its decomposition is
coincident with its death, and the dead matter
is thrown out of the body. New matter is
then added from the outer world. There is
thus a perpetual exchange between the dead
and the living worlds, which may be termed a
circulation of matter between the dead and the
living. Portions of the earth's surface now dead
were once part of the bodies of living beings,
and may again enter into the living state.

10. Form and Mode of Growth. As already
pointed out, living matter is jelly-like in its
consistence. It often changes its form, as
may be seen in an amoeba or in the colourless
cells in the blood. At the beginning of

LIVING ORGANISMS 25

existence, the typical form is nearly spherical,
as seen in the ovum, and also in many of the
minute cells of which the body is composed.
Living matter never assumes crystalline forms;
it does not grow like a crystal, by the deposition
of new matter on its surfaces, but by absorbing
matter into its substance and usually trans-
forming this into matter like itself. A crystal
does not transform, and it grows by the
deposition of new layers on its surface ;
living matter can transform, or assimilate,
and it can grow by the transformed matter
becoming part of its substance. It is re-
markable, however, that dead matter may
assume forms very similar to the forms of
living matter. In certain media crystallisable
substances may take on organic shapes, and
various mixtures of soaps, gums, etc., may
form a froth which, under the microscope, may
show forms very similar to that seen in living
stuff. In some circumstances even the move-
ments of living matter may be imitated.
Thus, a highly complex substance called
protagon can be extracted from yolk of egg
by hot alcohol. If a minute portion be

26 PRINCIPLES OF PHYSIOLOGY

placed under the microscope and a drop of
water be allowed to impinge on the edge of the
morsel, curious twisted or spiral structures
may be seen shooting out. These myelin
forms, as they are called, are instructive, as
showing lifelike movements in dead matter —
depending on changes in surface tension.
Some have even asserted that living matter is
essentially a kind of froth, and that the
structural forms are similar to those seen
when one blows a mass of soap bubbles
Walls and partitions may then appear,
and even one part may seem to be within
another, not unlike certain structures seen
in a thin section of living matter. Such
imitation- 'forms, however, do not imply life.
11. Evolutional History. A living being,
during the course of its existence, passes
through phases that follow each other in a
certain order. It originates in a germ which is
developed in a parent, that is, in a previously
existing being that has essentially the same
structure and properties. This germ, which
is known as the spore, seed, or egg of plants
and animals, is a cell, a comparatively simple

LiVING ORGANISMS 27

structure. After its separation from the
parent body, it is capable of independent exist-
ence, and, under favourable circumstances,
of developing into a new individual, in most
respects similar to that from which it derived
its origin Living beings form a continuous
series, from the first appearance of life on the
earth until now. The offspring have usually
characters which they have inherited from
their parents, but they may develop new
characters which may arise from new cir-
cumstances affecting them during their own
lives. If these characters, either inherited
or acquired, are transmitted to descendants,
the phenomenon is known as heredity. Each
living being shows a period during which
there is a maximum vital activity, when the
liberation of energy is greatest. During life
it passes by stages up to this period ; then,
after a stage of maximum activity, the
powers of the organism slowly decline.
During its life an organism undergoes change
of form, there is increase of mass, and it shows
increasing complexity of structure. These
changes, however, do not go on indefinitely.

28 PRINCIPLES OF PHYSIOLOGY

A condition of fully developed organization
is reached, for each kind of living thing,
reproductive processes occur, the processes
of life go on more slowly and less completely,
and finally some part of the machinery of
life breaks down, and death occurs. This is
the last stage in the evolution of that particular
organism. After death of the tissues of the
body, it is submitted to the action of external
agencies, both physical, chemical, and vital
(the vital being due to the activities of
micro-organisms of an inferior order), and
these ultimately reduce it to the simple
elements of which the body was at first com-
posed.

12. A living being is affected during every
moment of its life by the medium in which it
lives. The medium furnishes the material
necessary for its existence. Dead matter is
supplied to take the place of the living matter
that has died after having done its work.
External modes of energy, such as heat, light,
and electricity, act upon it, and energy is
supplied also by the chemical changes brought
about ultimately, but by many subsidiary

LIVING ORGANISMS 29

processes, by the interaction of the elements of
food and of the oxygen of the air. There is
thus action and reaction between the living
being and the conditions in which it lives.
These conditions are termed the environment.
The living being has, within limits, the faculty
of suiting itself to the surrounding conditions.
Such a power, which is a necessary condition
of the existence of every living being, is known
as its variability. It is the power of adaptation
to external conditions.

CHAPTER III

THE ACTIVITIES OF LIVING BEINGS

13. LIFE is a condition of activity. In the
body of one of the higher animals we see
activities manifested in various forms. Some
of these have already been referred to, but we
must now give a statement of those which
it is the special province of the physiologist
to explain.

(1) Animal Heat. The body of an animal
(we may leave plants out of this discussion,
although much that will here be indicated
also applies to them) has a certain mean
temperature. In so called warm-blooded
animals, such as the birds and mammals,
the temperature of the body varies only
through a few degrees, even although there
may be very considerable variations in the
temperature of the surrounding medium.
Thus the temperature of the body of a man,

30

ACTIVITIES OF LIVING BEINGS 31

taken by a suitable thermometer placed for
a few minutes in the arm-pit, varies in a
state of health only within a few fractions of
a degree above or below 98° Fahr. whether
the temperature be taken within the Arctic
circle or at the Equator. On the other hand,
the temperature of the body of a frog or of a
fish varies as the surrounding temperature
rises and falls. Such an animal is said to
be cold-blooded. The terms cold-blooded
and warm-blooded are not scientifically
appropriate. A warm-blooded animal, such
as a man or a dog, has a temperature that
is fairly constant, whereas a so-called cold-
blooded animal, like a frog or a fish, has
a temperature that varies considerably with
the temperature of the medium in which it
lives. But if the temperature of the air
surrounding a man's body is lower than 98.4°
F., then the body must be constantly losing
heat by radiation and conduction. The
questions at once arise : What is the origin of
this heat ? By what channels is it lost from
the body ? By what arrangement is the
temperature kept so uniform ? Are there

32 PRINCIPLES OF PHYSIOLOGY

heat regulating mechanisms ? These ques-
tions will be afterwards discussed. It is to
be noted that living matter can only perform
its junctions within a narrow range of tem-
perature.

(2) Motion. Animals move and parts of
their body move. They leap, run, or walk,
the chest moves in respiration, and the heart
beats. These movements are accomplished
rby the muscular tissues, which are the seat of
intense activities. Energy is here liberated
as motion. The physiologist has to study the
structure, nutrition, and the contractile func-
tions of muscular tissue. He finds that every
contraction of muscular tissue is associated
with active chemical changes occurring in the
tissue, by which there is a breaking down of
muscle substance, and the formation of
chemical substances of a simpler nature.
These chemical changes are intimately con-
nected with the breathing of the living muscle
substance, that is to say, they depend on
chemical phenomena in the muscle substance
which require the presence of oxygen and lead
to the elimination of carbonic acid and of other

ACTIVITIES OF LIVING BEINGS 38

waste matters. The muscle substance must be
repaired. This is done by nutritional changes
in the muscle. Materials are supplied in food,
which, after many chemical and physical
changes, are rebuilt into the muscle sub-
stance, thus renewing both the matter and
the energy that have been expended in
the muscle during its contractile activity.
The muscle liberates energy as heat, motion,
and, to a small extent, under the form of
electrical change.

(3) Secretion. This is a peculiar form of
vital activity occurring in glands, of which
there are many forms. The product of this
activity is termed a secretion. The essential
structures in a gland are a thin membrane on
one side of which we find living cells, and on
the other, and in intimate relation to these
cells, a network of minute blood vessels,
termed capillaries. From the capillaries a
fluid exudes from the blood, and this fluid
supplies nutrient material to the living cells.
These cells take such material into their sub-
stance and complex chemical processes then

go on. Each cell is a minute laboratory in

c

84 PRINCIPLES OF PHYSIOLOGY

which special substances are formed. The
cell gradually is filled with these substances and
then it bursts, liberating its contents, or in
some cases there seems to be a gradual removal
from the cell of the products of its secretion.
The matters thus collected from innumerable
cells become the secretion of the gland. We
may take as an example the secretion of
saliva. The cells of the salivary gland elabor-
ate the materials that form the secretion. In
particular, they form a peculiar body, known
as ptyalin, belonging to the class of ferments.
There is no ptyalin in the blood. It is formed
in the cells of the gland. Nor is it at once
formed from materials supplied by the blood.
There is at least one antecedent substance,
probably more than one, marking stages in the
gradual formation of ptyalin. In like man-
ner, the cells of the mammary gland elaborate
the complex fluid, milk, and those of the
pancreatic gland the remarkable bodies found
in the secretion of that gland, all of which are
ferments. Secretion, however, is essentially
a form of growth depending on the activities
of the secreting celL

ACTIVITIES OF LIVING BEINGS 35

(4) Nervous activities. All the various vital
activities are more or less controlled and
regulated by the nervous system, which may
be regarded as the master system of the body.
This consists of the brain, spinal cord, ganglia,
and nerves, but it may be more shortly de-
scribed as formed of nerve centres and nerves.
The nerves pass to and from the centres,
connecting up all parts of the body with those
centres. Nervous energy may originate in the
centres, — brain, or cord, or ganglia, — and it
may stream out along the fibres in the nerves
to various organs, such as muscles, glands,
blood vessels, and, in some animals (such as
the electric fishes), electric organs. This
energy, as to the nature of which we know
little, awakens the activities of those organs.
Under its influence, muscular fibres will
contract, the cells of a gland will secrete,
the walls of small vessels will alter their
calibre, and an electric organ will be the seat
of electrical changes. The centres, in their
turn, receive from the periphery of the body,
from the sense organs, and from all other
organs, nervous impulses that awaken activi-

36 PRINCIPLES OF PHYSIOLOGY

ties in the centres. These activities may
cause other impulses to stream outwards to
the various organs and thus stimulate them,
or they may, as in the higher brain centres,
be associated with various states of con-
sciousness, such as sensations, emotions or
intellectual and volitional processes. Thus
the whole body is bound together, and controlled
and regulated, by the nervous system.

CHAPTER IV

ORIGIN AND DEVELOPMENT OF THE
INDIVIDUAL

14. AFTER a general survey of some of the
fundamental characteristics of living beings, we
now turn our attention more especially to the
physiology of man, and the first question that
naturally presents itself is — How does he,
as an individual, originate ? At once the
answer will be given that he springs from
parents, a mother and a father. This easy
answer, however, gives no information, and
one may be rather startled by the statement
that he springs from structures of micros-
copical dimensions, that he owes his origin
to the combination of an egg or ovum with
a body called a spermatozoon. In this
he resembles the great majority of living
things. To appreciate, however, the wonder-
ful story of how this comes about, it is neces-

37

38 PRINCIPLES OF PHYSIOLOGY

sary to fix our attention on what is known as
a cel^ the first and smallest unit of structure
from which the tissues of the body are formed.
If we examine the body, say of a rabbit, we find
it is built up of various tissues. Thus we find
the flesh, consisting chiefly of muscular tissue,
the cartilages or gristles, the bones, the brain
and structures related to it (constituting the
nervous system), and the various glands and
internal organs, such as lungs, stomach and
liver. But if, by appropriate methods, such
as are used in the examination of tissues and
organs by the microscope, we pursue the
analysis farther, and more especially if we
study the tissues at various periods in their
development, we find that they all originate
from cells. A cell is a small bag or vesicle,
varying in size from the 1/6000 of an inch
to bodies just visible to the naked eye. Ante-
cedent even to cells, there is a still more
primitive substance known as protoplasm.
It is a jelly-like, colourless, or faintly yellow
substance, having often embedded in it
minute granules. It may either form large
masses, as in certain fungus-like forms, or it

ORIGIN AND DEVELOPMENT 39

may be in small portions, like the well-known
amoeba found in stagnant pools. One of its
most remarkable characteristics is that of
free movement, by which it may change its
shape from time to time. It has the power also
of absorbing organic matter from the medium
in which it lives, and of converting this into
protoplasm. It breathes : using up oxygen
and producing carbonic acid.

Protoplasm is always a constituent of
living cells. A cell may consist simply of a
bit of protoplasm, or it may consist of proto-
plasm having embedded in it a minute more
or less globular body known as a nucleus,
or it may have a thin envelope surrounding it
called the cell wall. A typical cell, therefore,
consists of a cell-wall, the protoplasmic
contents of the cell, and a nucleus. It can be
shown that the cell substance (or cytoplasm),
and also the nucleus, often show a network of
very fine fibres or a coiled fibre, and that the
contents are not structureless, as was at
one time supposed. The minute fibres, or
portions of fibres, found in the nucleus have
a special significance. These take up certain

40 PRINCIPLES OF PHYSIOLOGY

stains readily, and the material forming them
is termed chromatin or colourable stuff.
Further, the minute bodies thus stainable are
termed chromosomes, and it is remarkable that
the number of chromosomes is almost invaria-
bly the same for the cells of each species of
animal. The cell also contains matter that
is not stainable, or achromatin, as well as
matters formed from the substance of the
cells, such as droplets of fat, granules of a
starchy substance called glycogen, and other
bodies, as in secreting cells already mentioned.
There is usually a layer of absolutely struc-
tureless matter next the cell wall termed
hyaloplasm ; and it can be shown that certain
matters may pass through this layer while
others cannot do so. This is of importance
in connection with absorption of matters by
the cell and the elimination of matters from it
It is important to note that the cell is the
theatre of activities, of a physical, chemi-
cal, and vital nature, and that probably
all the phenomena of life may be manifested
by a cell. It often shows irritability, or the
power of responding to a stimulus, a property

ORIGIN AND DEVELOPMENT 41

which may be the beginning of psychical
states. These activities are all more or less
controlled and regulated by the nucleus. If a
cell be divided artificially so that one portion of
the protoplasm contains the nucleus, while
the other has no nucleus, the latter portion
soon dies, but the other portion remains alive,
and may grow and perform its functions as
before. Cells apparently secrete certain mat-
ters which collect outside the cells, forming
intercellular matter, so as to form a tissue,
such as cartilage or gristle ; in other cases,
this intercellular matter may form a fibrous
structure impregnated with earthy matter,
as in bone ; or the cells themselves may
be modified so as to form more complicated
tissues, such as muscle ; or the cells may cover
such surfaces as the skin, or, as secreting cells,
line the pouches of glands. All tissues are
primarily formed of cells, and the activities of
these tissues are the sum of the activities of
the cells. All cells arise from cells. Omnis
cellula e cellula.

15. The formation of the body is the result
of the union of two primitive cells, an ovum,

42 PRINCIPLES OF PHYSIOLOGY

or egg, derived from a female, and a sper-
matozoon, derived from a male parent. The
ovum is a small spherical vesicle about 1 /1 00
of an inch in diameter. Imbedded in its
protoplasm there is a large spherical nucleus,
termed the germinal vesicle, and, in the nucleus,
there is a still smaller body, the germinal
spot. Both the cell protoplasm and the
nucleus show a network of fine fibres, and in
the nucleus of the human ovum there are
chromosomes. The ovum is formed in a
special organ, the ovary, and at certain
periods the ovum is extruded into the Fallo-
pian Tube, a duct which leads to the uterine
cavity.

The male element, the spermatozoon, is a
minute body consisting of a head and a long
vibratile tail. The total length is about 1 /500
of an inch, while the head, which is the im-
portant part, is about 1/10 of the length.
The head represents the nucleus of a cell in
which the spermatozoon has been developed,
and it contains the all-important chromatm
The spermatozoa are formed in enormous num-
bers in the cells of a special organ, the testis.

ORIGIN AND DEVELOPMENT 43

16. It is remarkable that both the ova and
the spermatozoa appear in the same part
of the early embryo, a layer of germinal
matter, which is cut off, at an early period,
from the matter that is to form the body of
the individual, whether male or female. The
exact origin of the reproductive elements has
not been clearly established. It is suggestive
that immature ova are found in the ovary of
a female long before birth. There they lie
dormant, or undergo very slow changes till
puberty. The early origin of spermatozoa
has not been clearly established; the cells
that produce them are not active till the begin-
ning of adolescence. In the female the
extrusion of ova continues until perhaps fifty
years of age, but the production of sperma-
tozoa by the male may last through a long
life. Many intricate arrangements for the
nutrition and support of both are found in
the ovary and testis. Of themselves, at all
events in the higher animals, neither male
nor female element alone can originate a new
individual. The two must unite and blend
together This is fecundation. Antecedent

41 PRINCIPLES OF PHYSIOLOGY

to this event, however, both the sperma-
tozoid and the ovum undergo remarkable
changes, which have been studied in certain of
the simpler forms of animals, but while for
obvious reasons these phenomena cannot be
followed in a human being, there is every reason
to suppose they are of the same nature. These
phenomena consists essentially of various forms
of cell division, by which, in the case of the
spermatozoa, these bodies are increased four-
fold, while in that of the ovum, by a process
of splitting and separating of the chromosomes
in the nucleus or germinal vesicle, half of the
chromosomes are extruded and are practically
lost. Thus, suppose the number of chromo-
somes before these changes to be twenty, ten
are thrown out and ten are retained. Fecunda-
tion then occurs by the blending of the head
of the spermatozoid (containing chromosomes
from the male parent) with the germinal
vesicle of the ovum (containing chromosomes
from the female). It would appear that the
number of chromosomes in the fecundated
ovum is now doubled, that is to say, in the
case we have supposed, the number is again

ORIGIN AND DEVELOPMENT 45

twenty, but half are now maternal and half
are paternal. This is believed to be the
physical basis of heredity, as it is assumed
that hereditary characteristics are conveyed by
the chromosomes. This statement implies that
hereditary matter has been transmitted not
from parents only but from grandparents and
possibly from individuals of many previous
generations.

17. The fecundated ovum then divides
into two, each of the two into four, and so on
until a large number of cells are formed — and
by a remarkable series of processes, known as
Karyokinesis, each cell, when it divides,
transmits to its two descendants exactly the
same number of chromosomes, one half
representing the male while the other half
represents the female side. Thus, according to
modern theory, every cell in the body may possess
hereditary characteristics.

18. The early cells form certain layers from
which all the organs and tissues of the body
are developed.

The early embryonic tissue in which the
future being is formed is composed of two

46 PRINCIPLES OF PHYSIOLOGY

portions. One part is called the trophoblast.
It has to do with the formation of structures
for connecting the ovum with the mucous
layer of the uterus in which the embryo is
to spend the first part of its existence. The
other is the blastoderm, in which the future
being is to be developed. The blastoderm
divides into three germinal layers, an inner
called the endoderm, an outer named the
ectoderm, and between the two a third, the
mesoderm. The embryo at first consists of
only two layers, the endo- and ecto-derm, but
at a very early period the mesoderm makes its
appearance and is probably formed by the
other two. In turn, the mesoderm splits
into two layers, one of which becomes closely
adapted to the ectoderm, to form a thick layer,
the somatppleure, while the other clings to the
endoderm and becomes the splanchnopleure.
The somatopleure becomes the wall of the body,
and the splanchnopleure forms the outer wall
of the alimentary canal. Between the two
there is a space, the body cavity, which, in
full development, constitutes the pleural and
peritoneal cavities, in which lie the viscera of

ORIGIN AND DEVELOPMENT 47

the body. Several layers may combine in
the formation of the various organs and
tissues. A transverse muscular partition, the
diaphragm, divides the body cavity into two,
the thorax and the abdomen,

19. From the ectoderm are derived the
epidermic covering, the skin, and structures
such as nails and hair ; the epithelium of the
glands of the skin, of the mammary gland, of
the anterior part of the mouth, of part of
the alimentary canal at the anus, of the
anterior part of the nasal openings, of a
portion of the pituitary body, the enamel of
the teeth ; the whole of the nervous system ;
the epithelium of the sense organs, and a
portion of the suprarenal bodies. It is
important to observe that the nervous system
and the sensory layers of the organs of special
sense are formed from the outer layer of the
embryo.

20. Passing to the inner layer, the endoderm,
we find it develops into the epithelium of the
alimentary canal and the glands communicat-
ing with it ; the epithelium of the two Eusta-
chian tubes passing from the throat to the

48 PRINCIPLES OF PHYSIOLOGY

tympanum, or middle ear ; the lining of the
tympanum itself ; the epithelium of the
respiratory passages, larynx, trachea, bronchi,
and pulmonary air cells ; the epithelium of
the thymus and thyroid bodies ; and the
epithelium of the urinary bladder and of a
portion of the urethra.

21. From the epithelial portion of the
mesoderm, that is the somatopleure portion
of the mesoderm, are developed all the
voluntary muscles, the epithelium of the
Wolffian and Mullerian ducts (primitive excre-
tory organs) ; the epithelium of the excretory
tubules of the kidneys and Wolffian bodies ;
the epithelium of the lining of the body cavity,
sometimes called endothelium, the cortex of
the suprarenal body, and some of the cells
of the ovary and testis. Possibly the germ
cells are formed in this layer, but their place
of origin has not been conclusively established.
Lastly, from the mesenchyme, that is the
splanchnopleure layer of the mesoderm that
has become associated with the endoderm,
we find developed the connective tissues,
involuntary muscles, the spleen, the lymphatic

ORIGIN AND DEVELOPMENT 49

glands, lymphoid or adenoid tissue in various
organs, the lining epithelium of the heart and
blood and lymph vessels (endothelium) the
red corpuscles of the blood, and probably, but
not certainly, the white corpuscles of the
blood.

22. As already pointed out, the portion of the
ectoderm that takes no part in the formation
of the embryo is known as the trophoblast.
This structure by and by comes into relation
with the maternal tissues in the uterus and
an important organ is formed, the placenta.
By means of this organ the blood of the mother
is brought into close relation with the blood of
the offspring. A thin membrane and layers
of cells intervene, and both respiratory and
nutritional changes are carried on. The foetus
breathes by the placenta, receiving oxygen
from the mother's blood and giving up to it
carbonic acid. The placenta also supplies
materials for the nourishment of the foetus,
and no doubt proteins, carbo-hydrates, fats,
saline matters, and water are thus supplied,
for the growth of the foetal tissues. At this
period the tissues of the foetus are so nourished

50 PRINCIPLES OF PHYSIOLOGY

as to ensure constant growth, while its sluggish
life implies the production of a minimum of
waste products. Thus growth goes on steadily
and with astonishing rapidity. Tissue after
tissue and organ after organ are formed, not in
a definite order as regards time but contem-
poraneously, as if some kind of directive agency
were at work. There are even examples of
something like foreknowledge in the building
up of the fcetus. Stores of glycogen are sup-
plied for the nutrition of embryonic tissues.
Iron is collected in the body of the foetus,
from the mother's blood, so that an abundance
of this metal, all important for the develop-
ment of red blood corpuscles, is found in the
newly-born when in the new condition of exist-
ence it is nourished by milk, which contains
only a small supply of iron. Iron is needed,
but as the milk does not contain enough of iron
for the wants of the organism during lactation,
the child utilizes the iron that has been already
stored. In development, too, one of the most
remarkable phenomena is the formation of
organs in most of which tissues take part that
are supplied by different layers of the embryo.

ORIGIN AND DEVELOPMENT 51

Thus, as an example, the framework of the
liver is formed by connective tissue from the
mesoderm, while the hepatic cells are derived
from the cells of the endoderm and have the
same origin as the cells lining the alimentary
canal. To bring those two structures together
to form a liver implies growth from different
points and at the proper time.

23. Each tissue and organ has its heredi-
tary peculiarities. These are often obvious in
the features, the colour of the eyes and hair,
and the stature ; they are seen also in many of
those mental peculiarities that contribute to
the making of character and individuality ;
but they are not so evident in the arrange-
ments of individual organs. There can be
little doubt, however, that hereditary char-
acters may affect all the tissues and organs
of the body. They are not merely superficial.
All of these remarkable phenomena that lie
at the beginning of life are physiological
processes ; but science has not yet been able
to trace them from the physiological stand-
point. Interest in them, at present, is mainly
morphological, that is as regards the laws that

52 PRINCIPLES OF PHYSIOLOGY

regulate form in living mechanisms, but
physiological considerations cannot be ex-
cluded. How are we to explain the forces
in operation in producing the cleavages and
movements that are apparent ? How can we
account for the nutrition of the chromatin,
said to be the fundamental basis of heredity,
by which it multiplies itself ? Is there, as
some suppose, an inner world of molecular
movement in the chromatin, by which, influ-
enced by nutrition and by a kind of struggle for
existence and survival of the fittest, new com-
binations of chromatin-particles are effected so
as ultimately to produce individuals different
in some ways from their parents, or are the
phenomena only under the laws of chance like
the results of the rattle of the dice box ?
These are all profound questions lying at the
very basis of physiology.

24. Not many years ago it was not uncom-
mon for physiologists to think of the repro-
ductive elements, ova and spermatozoa, as
practically structureless, and to regard them
as being composed simply of granular, jelly-like
matter. Since then, owing to the improve-

ORIGIN AND DEVELOPMENT 53

ments in microscopes and in the methods of
microscopy, structure has been rendered
apparent where it was not supposed to exist.
Physicists had endeavoured to fix physiolo-
gists on the horns of a dilemma. Either an
ovum must have structure, which physiologists
at one time doubted, otherwise complicated
structures must have been evolved out of
what was structureless (which is inconceivable)
or, if the physiologists admit the existence
of structure, then the minute cubical capacity
of the fecundated ovum could not contain all
the organic molecules necessary to account
for the transmission of hereditary characteris-
tics. Since this criticism was made, in the
first place, structure in a fecundated ovum has
been admitted, and, in the second, we now have
more accurate estimates of the size of atoms
and molecules than was then available, with
the result that, even in the minute cubical
mass of a fecundated ovum, there is room
enough for all the molecules necessary to
transmit, by their combinations, all that is
required to account for even minute character-
istics in offspring. Further, the new physical

54 PRINCIPLES OF PHYSIOLOGY

conception of an atom, or molecule as matter
in which there is incessant movement, to
and fro and rotatory, makes it still less
difficult to conceive of a physical basis for
heredity.

CHAPTER V

DEVELOPMENT OF TISSUES AND ORGANS

25. WE have seen that the first organized
matter that forms the physical basis of life
is protoplasm. Then appears the more
specialized form, the cell, and from the
primitive cells the layers of the embryo are
developed. From these layers the various
organs and tissues of the future being are
produced. All embryonic tissues are very
similar to each other, consisting of protoplasm,
in which appear nuclei and cells in a more or
less rapid state of transition. From these the
various tissues are formed. The cells cover-
ing surfaces, either external, or those lining the
alimentary canal and the ducts and pouches
of the various glands, form a layer termed
epithelium. Such epithelial cells may be
close together to form a single layer, or the

layer may consist of cells three or four deep,
55

56 PRINCIPLES OF PHYSIOLOGY

in different degrees of development, those on
the surface being fully formed. It is to be
noted that all free surfaces are covered by
such cells, and it follows that matter
can neither enter the tissues of the body,
nor issue from them into the external world,
without passing through an epithelial layer.
Such matters do not, however, pass through
epithelium as a fluid passes through a filter,
but the matter is modified chemically and
physically by the epithelial cells.

26. Other cells become differentiated into
tissues that form, as it were, the framework
of the body, moulding the shape of organs, and
supporting their constituent structures. These
are called the connective tissues. This variety
of tissue is so abundant as to exist in every
organ, while it forms a framework for every
other tissue. Sometimes it is soft and con-
sists of delicate fibres forming networks or
membranes or cords (as in sinews), but it may
be infiltrated with earthy matter, and form
a hard structure of bone, and again it may be
hard, without earthy matter, in cartilage or
gristle. Lying in it, we always find cells in a

TISSUES AND ORGANS 57

condition of vital activity, and these cells
produce the intervening substance, such as the
fibres of ordinary connective tissue, the solid
basis of gristle or the hard substance of bone.
All such cells are engaged in forming a frame-
work to support other structures, and they
can also repair any injury to an organ, such
as may be caused by a cutting instrument.
Thus, a wound of the skin is healed and filled
up by connective tissues, as seen in a cicatrix
or scar. So abundant is connective tissue
that if we can imagine the body to be
immersed in a fluid which dissolved all the
tissues except connective tissues, we should
still have a cast of the body, spongy-like
in structure, formed of this tissue. It is
richly supplied with blood by fine capillaries
and by numerous lymphatic spaces and
channels for drainage of lymph. No doubt
it is the scene of active physiological changes.
27. The next tissue of importance is mus-
cular or contractile tissue, of which there are
several varieties. The masses of flesh we
find on the trunk and limbs are composed of a
variety of this tissue called striated muscle,

58 PRINCIPLES OF PHYSIOLOGY

on account of its striped appearance when
examined microscopically. It consists of a
mass of elongated nucleated cells, each an
inch or two in length, having pointed ends, and
its minute structure is so complicated that it
is still one of the puzzles of histologists. The
cell substance has become highly differentiated
into disk-like structures, which give the
tissue an appearance of striation, that is of
bands passing transversely across the fibre.
There is also a differentiation into longitudinal
structures called sarcostyles or fibrils, each of
which shows striation, due to the existence
of sarcous elements, or sarcomeres. When a
fibre contracts the sarcous elements contract
and a fluid substance, the sarcoplasm, is
pressed out in both directions till it is arrested
by a thin membrane, the membrane of Krause.
This membrane passes transversely across a
fibre and separates bundles of sarcostyles.
The sarcous elements are doubly refractive,
while the other parts between are singly
refractive. There appears also to be a very
fine reticulum, with longitudinal meshes,
n the fibre Another variety, called non-

TISSUES AND ORGANS 59

striated muscle, consists of elongated cells,
with no striation. It is found chiefly in the
wall of the stomach and bowel, in the ducts of
glands, in the walls of blood vessels, and in
the skin.

Finally, we find the power of movement,
or contractility, manifested by many cells,
usually isolated in a fluid, or embedded in a
tissue. Thus the white blood corpuscles
(leucocytes of several varieties), cartilage
cells, the cells in bone, connective tissue cells,
the cilia (hair-like structures) found on some
epithelial cells, are all contractile and are
capable of changing their shape. All forms
of contractile tissues are for purposes of
movement. Thus the movements of the
limbs in locomotion, and the movements of
the chest Avail in respiration, are effected
by means of striated muscles. Again, the
slow contractions by which, during diges-
tion and absorption, the food stuffs are
propelled along the alimentary canal, are
effected by non-striated muscle. The heart
beats, the changes in the calibre of the
smaller arteries by which the quantity of

60 PRINCIPLES OF PHYSIOLOGY

blood going to a part is regulated, movements
in certain ducts, as in the ureter (the duct
passing from the kidney to the bladder), the
contractions of the skin, are all effected by
non-striated muscle. The contractions of
cilia create a current in one direction, as in
those in the respiratory passages causing a
movement of air and mucus towards the
opening of the respiratory passage. The
leucocytes, by their contractions, can pass
out of the vessels into surrounding tissues,
and there they may seize hold of, kill, and
digest foreign organisms, such as many bacteria
and bacilli that cause disease. Probably, also,
by this power of ingesting foreign bodies,
they take part in processes of nutrition. All
contractile tissues, except the isolated cells,
are related to the central nervous system by
nerves that pass to and from these centres
to the contractile tissues. They are also
very richly supplied with blood vessels, and
they are nourished by the fluid that passes
out of the vessels, and bathes every fibre.
This fluid, called lymph, carries away all
excess of fluid, and also many substances in

TISSUES AND ORGANS 61

solution that are formed by the destruction of
muscle substance, or of chemical matters
in it, during contractile activity. Contractile
tissue constantly requires oxygen, and it
constantly produces carbonic acid ; this is
so, even during the resting of muscle, but,
when it contracts, much more oxygen is used
and much more carbonic acid is produced.
So complicated are the chemical processes
in contractile tissue that there is still uncer-
tainty regarding them.

28. The controlling and regulating tissue is
nervous tissue. It is found in the brain,
spinal marrow, ganglia, parts of the organs
of sense, and in nerves, and it consists of
nerve fibres and nerve cells. These will be
more fully considered when we treat of
nervous actions. Suffice it to say here
that nerve fibres generate and conduct what
we term a nervous impulse, a change, the
true nature of which we do not know.
Such an impulse, issuing from a nerve
centre, such as a portion of the spinal
cord, may travel to a muscle and cause the
striated tissue to shorten, when there may

62 PRINCIPLES OF PHYSIOLOGY

be movement of a limb ; or it may, when
it reaches the non-striated muscle in the
bowel, cause slow ring-like movements of
the tube (peristaltic) ; or it may affect the
number and strength of the heart beats, or it
may cause the walls of small arteries to con-
tract and thus regulate the amount of blood
flowing through them ; or it may stimulate
the activity of a secretion, as seen, for example,
in the increased flow of saliva when a sapid
substance is in the mouth, or even when
the sight or thought of delicious food has
the same effect. The electric discharge of an
electric fish is also under the control of the
nervous system, which also appears to affect
the light of the firefly, glowworm, and even
the light of the luminous organs found in some
fishes that live in the profound darkness of
the depths of the ocean. Finally, in the nerve
cells that form the main part of the nerve
centres, such as the brain and spinal cord,
there are molecular changes of which we know
next to nothing, and yet on these all nervous
activities depend, even those associated with
mental processes.

TISSUES AND ORGANS 63

29. It would seem that during countless
ages evolution has slowly built up a great
variety of animals. This evolutionary process
has also affected more or less every tissue.
We may detect primitive types of tissue, such
as we find in the embryo, in the tissue of the
placenta and umbilical cord, in the cells
between the bodies of the vertebrae, in the
vitreous humour of the eye, in the so-called
lymphoid tissue found in various organs,
and in connective tissues generally. Cartilage
or gristle has preceded bone. Non-striated
may be regarded as more primitive than
striated muscle. Even some striated muscles
seem to be more primitive than others. These
muscles are usually pale, but certain muscles,
such as the semi-membranous muscle in a
rabbit's leg, are red. Red muscles contract
more slowly than pale muscles, and their
structure seems to be of a lower type. Nervous
tissues have passed through many forms, until
we reach the highly complicated cells of the
nerve centres. The nervous elements of the
sense organs also show differentiation as we
pass from lower to higher forms. Thus the

64 PRINCIPLES OF PHYSIOLOGY

retinal elements of the eye of a codfish are
very different from those in the human retina.
Little attention has yet been paid to the
evolution of tissues, and the question of
whether it has been brought about by the
agency of external circumstances on a particu-
lar tissue, or by the influence of one tissue on
another, cannot yet be answered. It is strik-
ing, however, to observe that evolution, which
depends on physiological processes, affects not
merely the outward form but even the tissues
that build up the body of an animal.

CHAPTER VI

MATTER AND ENERGY IN THE LIVING
BODY

30. Matter and chemical processes. As has
already been pointed out, the phenomena of
life depend on chemical changes occurring in
the body. These changes are largely oxida-
tions, that is the union of oxygen with cer-
tain constituents of the body, and decomposi-
tions, that is the splitting up of more complex
chemical substances into simpler ones. There
are also, to some extent, reductions, that is,
the taking of oxygen from chemical constitu-
ents ; and there are syntheses, the reverse of
decompositions, or the building up of com-
plex substances from simpler ones.

81. We are still ignorant of the exact
nature of many of the chemical processes
occurring in living tissue, but they may be
shortly noticed.

B 65

66 PRINCIPLES OF PHYSIOLOGY

(1) Oxidation is the most common chemical
reaction. By continuous processes of oxida-
tion complex bodies are split up into simpler
ones. Thus by oxidation, protein, such as
exists in white of egg, may be split up into
leucin, tyrosin, glycine, and the fatty acids ;
uric acid into urea, allantoin, oxalic acid and
carbonic acid. Oxidation has been carried
out by the chemist, with the production of
chemical substances the same as those found
in the fluids and tissues ; and the inference
is that in the living body they are also pro-
duced by oxidation. But in living matter
the processes are obscure, and there are
probably intermediate steps still unknown.
There can be little doubt that oxidations
occur almost wholly in the tissues ; but
we must avoid taking too mechanical a
view of the nature of oxidation in living
matter. There is no such phenomenon as
the direct union of oxygen with carbon, or
with hydrogen, as in burning a candle. The
combustion of a candle will always yield, for a
given weight, the same amount of carbonic
acid and of water, and the same amount of

MATTER AND ENERGY 67

oxygen will be used up. But there is no
parallelism in the so-called oxidation in living
stuff. Oxygen may disappear in the process,
and the amount of combustion products cannot
always be accounted for by the amount of
oxygen used. Oxidation in living matter is
a complicated process.

(2) Reduction is due to the abstraction of
oxygen. It plays an important part in the
chemistry of plant life, but it is not so common
in the animal body. Fats may be formed
from carbo-hydrates, as in the feeding of
pigs with starchy matter ; much more fat is
formed than can be accounted for by the fat
in the food. But fats presumably are formed
from carbo-hydrates (starches, sugars, etc.),
by the abstraction of oxygen. Not a few
substances passed through the body suffer
reduction. Thus the iodides and bromides
of the alkalies are formed from iodates and
bromates, and malic acid (as in fruits), becomes
succinic acid.

(3) Decompositions frequently occur, when
complex substances are split into simpler
ones. Thus taurocholic acid, the acid of one

68 PRINCIPLES OF PHYSIOLOGY

of the salts found in bile, taurocholate of soda,
may be resolved into its two constituents,
taurine and cholalie acid. Sometimes water
is removed from a compound, and the remain-
der then decomposes. Thus creatin, a sub-
stance found in flesh- juice, by the abstraction
of water becomes creatinin, which is voided
in the urine. On the other hand there is a
reverse process. Water may be first taken up in
chemical combination, and a new substance
then formed. Thus urea, found in the
urine, combines with water, and there is then
a re-formation of the molecules to form car-
bonate of ammonia.

(4) Living matter, in certain circumstances,
may combine with oxygen, and possibly with
other bodies, not by a chemical combination,
but by a physical process depending on tem-
perature and pressure. This has not been
absolutely proved with protoplasm, but it
is suspected. The colouring matter of the
red blood corpuscle, a highly complex sub-
stance called haemoglobin, combines with
oxygen to form a compound known as oxy-
haemoglobin. The amount of oxygen taken

MATTER AND ENERGY 69

up varies directly as the pressure and inverse-
ly as the temperature. Thus, at the same
temperature, by lowering the pressure by
placing the oxy-haemoglobin in the partial
vacuum of an air pump, the compound
gives off the oxygen, without itself suffering
decomposition. When the pressure is raised,
the oxy-haemoglobin again takes up oxygen.
This process, known as dissociation, depends
on physical conditions. It plays an important
part in respiration.

(5) By synthesis is meant the building up
of complex chemical substances by the union
of simpler bodies. This has been accomplished
by the chemist, and, as already stated,
numerous organic bodies have been formed
artificially in the laboratory, such are urea,
hippuric acid, glycine, taurin, creatin, glu-
cose, and numerous organic acids, such as
oxalic, lactic, succinic, benzoic, propionic,
acetic, and formic acids. Even bodies
resembling proteins have recently been
formed synthetically, and it is probable
that, by following out synthetic processes
that are suggested by theory, proteins of

70 PRINCIPLES OF PHYSIOLOGY

higher complexity may yet be formed. It
is not easy to give examples of syntheses in the
animal body. If benzoic acid is given in
food or as a drug, it unites with glycine,
probably in the liver, to form hippuric acid,
with the elimination of a molecule of water
Many organic acids may thus be built up.
Thus aromatic bodies unite with sulphuric
acid, and conjugated sulpho-acids thus formed
are eliminated by the kidneys. No doubt
synthetic processes may also build up fatty
phosphorized substances existing in nervous
matter, haemoglobin (the colouring matter of
the red corpuscles), and even proteins.

(C) Enzyme or Ferment Action. One of the
most interesting chapters in the history of
scientific discovery has been that of the
nature of fermentation. Fermentation and
putrefaction have been known from early times,
but their true nature has been discovered only in
comparatively recent years. It is now known
that both are connected with the life-history
of micro-organisms, such as in the ordinary
fermentation of sugar into alcohol, carbonic
acid, and other substances, by the agency of

MATTER AND ENERGY 71

various kinds of yeast cells or toruiae, and the
putrefaction of dead nitrogenous matter by
the activity of various bacteria. A recogni-
tion of these facts, and of the part played by
micro-organisms in many diseases, has led to
the evolution of the vast realm of knowledge
now known as bacteriology. Physiologists
have long been acquainted with the existence
in the body of ferments, such as the ptyalin
of the saliva and the pepsin of the gastric
juice, but it is only in recent years that there
has been an adequate recognition of the part
played by ferments in many physiological
processes. It is now known that all ferments,
or enzymes, as they are now called, are formed
in the interior of cells. For a long time it was
held that the plant known as the yeast cell
effected fermentation in the juice of the grape
or in a solution of sugar by its vital activity,
and this view was favoured by the fact that
durng fermentation there was a remarkable
multiplication of the cells of the yeast
It is now known, however, that even this
fermentation is caused by an enzyme (zymase)
formed in the interior of the yeast cell.

72 PRINCIPLES OF PHYSIOLOGY

In a similar way all enzymes are formed in
cells, as, for example, ptyalin in certain cells
of the salivary glands, and pepsin in certain
cells in the tubular glands in the mucous
membrane lining the stomach.

32. The enzyme, however, is preceded in
the cell by an enzyme-forming substance, a
zymogen, as it is called, and while the cell is
secreting, matter appears in the form of small
granules. Thus ptyalin is preceded by pty-
alinogen, pepsin by pepsinogen, and so on.
It would appear that just when the secretion
is poured out the zymogen is changed into
the enzyme, and the enzyme at once begins
to act. Each enzyme has a limited field of
activity. Thus three are required to modify
the three varieties of di-saccharides, cane
sugar, milk sugar (lactose) and maltose, one
and only one for each sugar. The activity of
enzyme is greatest at about 40° C : at about
50° C. the ferment is destroyed Extreme
cold arrests the activity, but it does not appear
to injure it, as it will again act at, say, 40° C.
One remarkable feature of the action of an
enzyme is that only a small amount is neces-

MATTER AND ENERGY 73

sary, and at the end of the process the amount
of enzyme is the same as at the beginning
If the enzyme is used up, or if a portion
of it is used up, there must be a process
by which the enzyme is reconstructed. To
avoid this difficulty, it has been supposed that
the enzyme acts catalytically, that is, merely
by its presence. It is difficult to imagine that
any substance can modify a chemical product
merely by its presence. This idea arose from
the fact that the enzyme appeared to be
unaltered in the process. The chemist is also
aware of chemical processes influenced by the
presence of inorganic substances. Thus a
mixture of oxygen and hydrogen immediately
explodes when brought into contact with
platinum black. If so, we may imagine that
some kind of vibratory action is communi-
cated to the molecules of the fermentable
matter from the enzyme, and that this vibra-
tion causes the change in the substance. The
analogy is that of sympathetic vibrations
between two tuning forks of the same pitch.
Thus a fork Ut4 will, if caused to vibrate
by bowing, at once set in action the prongs of

74 PRINCIPLES OF PHYSIOLOGY

another fork, also Ut4, even if the two forks
are at a considerable distance from each
other As we know nothing of the chemical
constitution of enzymes, except that they
are proteins, this can only be a conjecture,
but it is to be borne in mind that proteins are
very unstable. Enzymes may act alone or
they may apparently be stimulated by other
enzymes or by the presence of other sub-
stances. In chemical reactions we have to
consider the element of time, or what we may
term the velocity of the reaction. It would
appear that all so-called catalytic actions,
including the action of enzymes, have the
effect of quickening the velocity of the chemi-
cal changes involved.

33. As already pointed out, enzymes are
formed in cells. Cells may be frozen and then
pounded into a paste. Enzymes are thus set
free, and at the proper temperature they will
manifest their usual activities. This shows
that they do not depend on the life of the
cells. There can be no doubt that as almost
all cells contain enzymes, they take part in
nutritional processes, by exciting changes in

MATTER AND ENERGY 75

the protoplasm of the cell, or possibly in the
substances stored in the cell. They may thus
carry on metabolic changes, during the life of
the cell, and they may even cause destruction
of the cell after death, by a kind of auto-
digestion, or autolysis.

34. Most enzymes are hydrolytic, that is
to say, we may represent their action by the
addition of water to the fermentable matter
and then a decomposition. Thus cane sugar
plus water plus the enzyme, is changed into
dextrose and levulose, two other varieties of
sugar. But other enzymes are believed to
carry oxygen to the tissues. These have
probably to do with respiratory processes.
They are termed oxidases.

35. Enzymes may be readily classified
thus : —

(1) Amylolytic — Change polysaccharides
such as starch into sugar. Example : Ptyalin
of saliva and the diastase of plants.

(2) Invertins — Change disaccharides into
mono-saccharides. Ex. : Invertase of intestinal
juice, which changes cane sugar into dextrose
and levulose.

76 PRINCIPLES OF PHYSIOLOGY

(3) Steatolytic or Lipolytic — Decompose fats
into fatty acids and glycerine. Ex. : Steapsin
or Lipase of pancreatic juice.

(4) Proteolytic — Change proteins into pro-
teoses, peptones, polypeptides, and at last into
amino-acids. Ex. : Pepsin of gastric juice ;
trypsin of pancreatic juice.

(5) Peptolytic — Decompose proteoses and
peptones into polypeptides and amino-acids.
Ex. : Erepsin of intestinal juice.

(6) Blood ferments — Cause clotting of blood.
Ex. : Thromhin (fibrin ferment) ; rennin of
gastric juice converts caseinogen of milk into
casein.

(7) Ferment of ferments — Enzyme that stim-
ulates the formation and action of the trypsin
of the pancreatic juice. Ex : Enterokinase of
duodenum.

(8) The acid chyme, when it leaves the
stomach, leads to the formation of an enzyme,
secretin, which is absorbed into the blood and
stimulates the secretion of pancreatic juice,
Probably other chemical substances act in
a similar way, on various secretions. These
are called hormones

MATTER AND ENERGY 77

36. Matter and Energy. All chemical
phenomena are associated with changes in
energy, one of the great conceptions of modern
physical science. Energy may be latent or
locked up in a chemical substance, and it is
then said to be potential. Thus, take any oil
as an example. An oil contains carbon,
hydrogen and oxygen so united as to form a
complex substance, say the olein of olive oil,
each molecule of which has a definite chemical
composition. The oil (or the olein), however,
is conceived to be associated with energy in
a latent state, that is to say, the energy that
binds the atoms into its molecule is there
locked up, and so long as it is so, the molecule
is chemically inert. But if it be oxidized, that is
if it be burned in a suitable contrivance, say a
lamp, the oxygen of the air unites with the
carbon of the oil to form carbonic acid, and
with the hydrogen, to form steam or water.
The carbon appears in the form of soot.
But during the burning, energy appears as
heat, and the heat, by a suitable machine,
might be converted into motion, and do
work by lifting a weight and overcoming the

78 PRINCIPLES OF PHYSIOLOGY

friction of a train of wheels. While the energy
is thus doing work it is said to be actual or
kinetic. The complete combustion of a
given amount of olein would produce a certain
equivalent of heat, and the heat, again, might
be transformed into a certain equivalent of
motion. There is a fixed quantitative rela-
tion between the two modes of energy. Thus
physical science tells us that a unit of heat is
the amount of heat that is required to raise
the temperature of 1 gramme (15.4324 grains)
from 15° to 16° centigrade, and the unit of
work is the grammetre, or the amount of work
expended in lifting 1 gramme to the height of 1
metre (39.37 inches). Apply this to a special
case ; a decomposition liberating heat, develops
1 heat unit, and this heat, if it does mechanical
work, will perform 424 grammetres of work.
Thus 1 unit of work may be converted into
1 unit of heat, and conversely.

37. Energy therefore may be either potential
or kinetic. When simple substances are
combined to form complex ones, energy
becomes latent or potential, and when a
complex substance is split up into simpler

MATTER AND ENERGY 79

ones energy becomes kinetic; it may appear,
for example, as heat or motion. In the case
we are considering, it is possible to determine
with accuracy the energy the oil contains, or,
in other words, the heat produced by its
combustion ; this amount of heat is conceived
as kinetic energy ; and if it were possible, by
a synthetic process, so to combine the carbon,
hydrogen, and oxygen as to re-form the olein,
the same amount of energy would have to be
expended as was liberated by decomposition.
In any such system of operations the sum of
the energy at the close would be the same as
at the beginning.

38. Chemical Substances. We are now in
a position to consider from the chemical
point of view, the matter of which the body is
composed. The chemical elements in living
matter have been referred to in section 7.
These elements are combined to form chemi-
cal compounds, divided into organic and
inorganic. Organic compounds are again
classified into nitrogenous and non-nitrogen-
ous. The nitrogenous are the more important ;
they are necessary for the constitution of

80 PRINCIPLES OF PHYSIOLOGY

protoplasm. It must be observed that a
chemical analysis of living matter is not
possible, because, in the processes to which it
must be subjected, the condition we associate
with life disappears. The living matter is
killed by the attempt at analysis, so that what
we are able to analyse is dead matter that
was once alive. Suppose a chemist is asked to
reveal to us the chemical constituents of a
muscle, he might be able to enumerate the
elements of which it was composed. This
would teach us very little. But during the
analysis it would be found that numerous
more or less complicated chemical substances
appeared, and that these could be arranged
into groups, the members of which showed
certain characters in common. In this
way we learn that organic matter is built
up of certain compounds called proximate
constituents, or principles, already referred to
These are proteins, carbo-hydrates, and fats,
and along with these we find many other
substances which are derivatives of these three,
along with various saline substances and water.
39. The proteins are bodies of highly

MATTER AND ENERGY 81

complex chemical constitution. They all
contain about 16 per cent, of nitrogen, along
with carbon (more than half their weight),
hydrogen, oxygen, and usually a small amount
of sulphur or phosphorus, or both. Proteins,
a typical example of which we find in the
albumen in white of egg, are essential in
protoplasm, and they are more intimately
associated with the phenomena of life than
any of the other proximate principles, in the
sense that wre never find vital phenomena
without them, and that vital phenomena are
never manifested by carbo-hydrates, fats, saline
matter, or water, either alone or in combination.
Proteins are usually colloidal or glue-like, and
are non-diffusible through animal membranes.
A colloid does not form a true solution, but in a
fluid it forms a kind of emulsion consisting of
minute particles or globules suspended in the
fluid. (Such an emulsion- colloid is termed
a gel, but there are colloids, having much
finer particles, and which have different
properties. Such are called sols. Proto-
plasm, alive, is probably of the nature of a
sol.)

82 PRINCIPLES OF PHYSIOLOGY

Of the true chemical structure of proteins
we know little, but it has been shown that
by various agencies they split up into numer-
ous simpler bodies which also may be arranged
in groups. There seem, as it were, to be
lines of cleavage, so that the complex pro-
teins, under the influence of acids, alkalies,
high temperatures, and various enzymes,
decompose into acids, bodies of a fatty
nature, aromatic bodies, — which all contain
nitrogen, — and bodies that belong to the carbo-
hydrate group, — containing no nitrogen, — such
as starch and sugar. Such bodies are pro-
duced when proteins are split up, whether
it be by the processes of the chemist in the
laboratory, in the process of digestion under
the action of the digestive enzymes, or in
putrefaction as carried on by many micro-
organisms, and more especially by the Bac-
terium termo, a minute organism found
wherever there is decay. Proteins are ulti-
mately resolved into certain ammoniacal
compounds and urea, a substance abundant in
the urine.

40. The carbo-hydrates are the starches

MATTER AND ENERGY 83

and sugars. They consist of carbon, hydrogen
and oxygen, the two latter elements being in
the proportions that form water, that is,
two of hydrogen to one of oxygen, hence the
somewhat inappropriate name. They contain
no nitrogen. They are usually classified into
the polysaccharides, such as starch and glyco-
gen (an animal starch found in the liver),
monosaccharides, such as dextrose, glucose or
grape sugar ; and disaccharides, such as cane
sugar, lactose, and maltose. When cane
sugar is inverted, it takes up water and is
changed into equal parts of dextrose (grape
sugar) and levulose (fructose). By hydro-
lysis of starch various forms of dextrin are
formed. Cellulose, as found in the cell-
walls of plants, is also a carbo-hydrate.
Carbo-hydrates, by various chemical agencies,
may also be resolved into simple substances,
and ultimately into carbonic acid and water.
41. The Fats consist of a combination of
a fatty acid and glycerine. They consist of
carbon, hydrogen, and oxygen, but the amount
of carbon present in proportion to the oxygen
present is much greater than in carbo-

84 PRINCIPLES OF PHYSIOLOGY

hydrates. When oxidized, as by burning, they
are resolved into carbonic acid and water,
with a great evolution of heat. The chief fats
are tri-stearin, tri-palmitin, and tri-olein.
When a fat is acted on by lipase (an enzyme),
it hydrolyses and splits into a fatty acid and
glycerine. If a fat is acted on by an alkali
a soap is formed and glycerine is liberated.
42. Along with proteins, carbo-hydrates, and
fats, there are various salts, such as chloride of
sodium (common salt), chloride of potassium,
various phosphates of soda, potash, lime, and
magnesia. In the ash of organic matters we
also find sulphur and iron compounds, but these
are derived not from inorganic compounds
of these elements, but from decomposition of
the proteins It is doubtful if any of these
inorganic salts exist during life in a free state ;
it is more than probable that they are usually
combined with organic bodies, and that in
this way they take their part in vital pheno-
mena. The proportions of the various salts,
as determined by chemical analysis, is very
uncertain. It may be that certain saline
matters are simply dissolved in the colloidal

MATTER AND ENERGY 85

living matter. There is, however, another
way in which they may be taken up, when
they are not dissolved, but pass into the
colloidal matter in virtue of some affinity for
it. This process is called adsorption. The
electrical state of the colloid influences this
process. Adsorption plays an important part
in physiological processes.

43. Finally we have water, the general
solvent, and the medium by which the mole-
cules of the other bodies are brought so close
together as to permit of those reciprocal
actions on which life depends. About two-
thirds of the weight of the body consists of
water.

44. Chemical Phenomena of Plant Life.
We can now form some conception of the
relation of matter and energy in the living body,
and we shall be assisted if we consider the
chemical phenomena of plant life and contrast
these with what happens in an animal. A
plant requires ammoniacal salts, water and
carbonic acid. These it derives from the
soil and the air, and ammoniacal com-
pounds that are mainly the result of chemical

86 PRINCIPLES OF PHYSIOLOGY

operations in the animal body. The proto-
plasm of the plant combines these with oxygen,
forming more complex chemical compounds.
Thus by means of chlorophyll, and under the
action of the energy of light, it decomposes the
carbonic acid of the air, retaining the carbon
and returning the oxygen to the air. The
carbon is then united with oxygen and hydro-
gen to form starchy substances, which, by the
action of an amylolytic ferment (diastase), may
be changed into sugars, In a similar way, the
ammoniacal bodies are used up to form pro-
teins. All this is done by the protoplasm of
the plant cell, and there can be little doubt that
the formation of these bodies is the result of
chemical operations in the protoplasm, which
is alive. To do this it must have oxygen, and
it must get rid of the waste body, carbonic acid.
This constitutes the true respiration of a plant,
and must not be confused with the chlorophyll
action above referred to. The plant thus
transforms the kinetic energy of the sun's
rays into the potential energy stored up
in the starch and in the protein matter
in its cells, Fats may also be formed. The

MATTER AND ENERGY 87

plant protoplasm, however, while it performs
this operation, also, in connection with its
own special activities, sets free kinetic energy.
Thus certain of the parts of plants produce
heat, and energy may appear as motion,
when rootlets press through the soil, or when
certain parts move. Still the main relation of
plant life to energy is that it stores it up, or
renders it potential.

45. Chemical Phenomena of Animal Life.
The activities of an animal are mainly of an
opposite kind. The animal lives on plants
or upon the tissues of other animals. Animal
protoplasm cannot exist on ammoniacal
compounds, water, and saline matters alone.
It has little or no power of forming those
into more complex substances. But it
takes proteins, carbo-hydrates, and fats,
and along with saline matters and water it
builds these up into its own protoplasm. It
may possibly use them to some extent
directly, that is to say, without incorporation
into its protoplasm, but this is doubtful.
It is probable that there is a true incor-
poration, but, before incorporation, the

88 PRINCIPLES OF PHYSIOLOGY

proteins, carbo-hydrates, and fats must be
modified by digestive processes, So far the
animal protoplasm, like that of the plant,
has been storing energy There is now a
reversal of the operation Under various
stimuli, which may be the nervous impulse,
or a mechanical, thermal, or electrical
stimulation, the protoplasm either contracts
(as in muscle) or is the seat of chemical
operations (as in a secreting cell or an electrical
organ), and energy is set free as motion and
heat, or, it may be, luminous or electrical
energy This implies decompositions and
oxidations, and requires oxygen from the air.
The splitting up of the complex protoplasm
causes the formation of simpler bodies. These
may be again and again further oxidized into
simpler compounds, always with the evolution
of energy, as heat, until ultimately we reach
simple ammonia-like bodies, urea, and water.
Thus the protoplasm of animal cells is chiefly
engaged in the liberation of potential into
kinetic energy. Both plant and animal take
part in both processes. In the plant there
are oxidations as well as reductions, but

MATTER AND ENERGY 89

mainly reductions ; in the animal there are
reductions as well as oxidations, but mainly
the latter. Both, as in processes of develop-
ment, convert potential into kinetic energy,
but in the plant the conversion is mainly from
kinetic into potential, while in the animal
the action is far and away a passage from
potential into kinetic energy. Thus the plant
world is, physiologically, the complement of the
animal world

CHAPTER VII

INCOME OF MATTER. THE ABSORPTION
OF FOOD STUFFS

46. As all forms of vital activity cause a
certain amount of tear and wear owing to the
breaking down of living matter, or, in other
words, the decomposition of complex organic
substances into simpler ones, — usually accom-
panied either with the withdrawal of oxygen
(reductions) or with the union of oxygen with
oxidizable substances (oxidations), — matter
must be supplied in the form of food. Food
stuffs however, as a rule, are very unlike the
tissues of the body. Observation also shows
that animals may live on food stuffs that are
very unlike in appearance. Thus an ox can live
upon grass, a horse on hay and oats, a rabbit
on turnips or carrots, a tiger and other flesh-
eating animals on flesh of various kinds.

Man is so constituted as to find a mixed diet
90

INCOME OF MATTER 91

most suitable. All mammals begin their
existence on milk. The tissues of a chick
are built up out of materials contained
within an egg. If, however, we analyze
food stuffs, or diets that are known from
experience to suit all dietetic requirements, we
find they always contain representatives of
the five proximate constituents found in
the tissues of the body, and which we
have considered. Thus a suitable dietary for
almost any animal, and certainly for men,
always contains proteins, carbo-hydrates, fats,
saline matters and water. Other substances,
such as the condiments that are often added,
are merely adjuncts to the diet. Thus milk
contains more than one protein substance,
the chief one being caseinogen, which yields,
when acid or rennin is added to the milk, a
protein, casein, the chief constituent of curd ;
a carbo-hydrate as sugar of milk ; a fat,
or rather several fatty matters that all together
form butter ; various salts (chiefly chloride of
sodium and phosphate of lime) ; and water.
These proximate constituents are found in
varying amounts in different articles of food

92 PRINCIPLES OF PHYSIOLOGY

met with in dietaries. Thus, butcher meat
abounds in protein and fat, potatoes in starch
(a carbo-hydrate) ; and vegetable oils and
animal fat are rich in fat. By combinations
of these, a suitable dietary is formed, and
experience has taught mankind, even in
savage conditions, empirically to combine
such substances. Further, science has shown
that a suitable dietary supplies the requisite
amount of carbon and the requisite amount
of nitrogen to make up for the daily loss of
carbon eliminated chiefly by the lungs, as car-
bonic acid, and of nitrogen thrown out by the
kidneys mainly as urea.

47. In order to become incorporated with
the living tissues, food stuffs must pass
through a series of elaborate physical and
chemical processes, the object of which is
to render them soluble and suitable for ab-
sorption into the blood. These processes
constitute Digestion. The food is broken
down and mixed in the mouth with saliva
so as to form a pulpy mass. Such matters
as saline substances may be at once dissolved,
and the whole process is facilitated by the

INCOME OF MATTER 93

heat of the mouth. Mastication is a physical
process carried on by the movements of the
jaws bearing the teeth. Saliva is a fluid
poured forth from three pairs of salivary
glands and by numerous small glands in
the membrane lining the various parts of the
mouth. Chemically, the saliva acts only on
carbo-hydrates in the form of starch: it has
no chemical action on proteins or fats. The
saliva, in addition to being a watery solvent,
contains an enzyme called ptyalin, which con-
verts starch into dextrose or grape sugar, thus
rendering the carbo-hydrate soluble. The
saliva also lubricates the mouthful with
mucus, and thus facilitates swallowing.

48. The food is then swallowed (Degluti-
tion) and by a muscular mechanism (con-
trolled by nerves) it is prevented from escaping
by the mouth, or into the nose by the posterior
apertures of the nostrils, or into the chink
between the true vocal cords which is the
entrance into the trachea, or windpipe, and
the respiratory passages. It is propelled
into the gullet (oesophagus), and carried into
the stomach by a series of contractile move-

94 PRINCIPLES OF PHYSIOLOGY

ments. The greater part of this nervo-muscu-
lar mechanism is beyond the control of the
will, after the food has passed sufficiently far
into the mouth, and so exquisite are its adap-
tations that only when food is swallowed
hurriedly, or with great gulps of liquid, is there
any danger of the matter entering the wrong
passage.

49. In the stomach, which is simply a special
enlargement of the alimentary canal, the food
is subjected to three processes : — (1) The
action of a temperature of about 98° F. ;
(2) a churning-like motion produced by slow
contractions of the muscular walls by which the
food is thoroughly mixed with the special
secretion of the stomach, the gastric juice ;
and (3), the chemical action of the gastric
juice itself. This juice is secreted by numerous
tubular glands in the mucous membrane,
It is a clear watery fluid containing a
minute quantity of various salts in solution,
a small amount (*2 per cent.) of hydrochloric
acid, and a special enzyme, pepsin. It is only
secreted in ordinary circumstances when food
enters the stomach, and by the contractions

INCOME OF MATTER 95

of the walls it is thoroughly mixed with
the contents. The action of pepsin is on
proteins, converting these into a more special-
ized form of protein, termed peptone ; and
in this action it is assisted by the free hydro-
chloric acid of the gastric juice. The juice,
by acting on the walls of the cells in the food
stuffs, liberates fatty matters, or granules of
more or less cooked starch, and thus these are
prepared for further digestion. Saline matters,
that may have escaped the solvent action of
the saliva, are dissolved. Protein food stuffs,
as in cooked butcher meat, are disintegrated
into fibres and small morsels; these are
then acted on by the pepsin and hydro-
chloric acid. The result is the formation of
a semi-digested mass, the chyme, which, as it
is formed, escapes through the pyloric opening
into the first portion of the small intestine, the
duodenum. During the digestive process in
the stomach, the orifices at the lower end of the
oesophagus and at the beginning of the small
intestine, the pyloric opening, are tightly
closed by sphincters. Thus a portion of any
protein in the food is converted into simpler

96 PRINCIPLES OF PHYSIOLOGY

and more soluble forms of protein called
peptones, and the mass, containing, in addition
to peptones, undigested protein matters,
sugars, starch-granules that have escaped
the action of the saliva, fats in a more or less
fluid state, salts in solution, constitutes
the chyme. It is doubtful if absorption
to any extent occurs in the stomach. The
free hydrochloric acid of the juice may
cause some proteins to swell and become
gelatinous-looking, forming what is called
syntonin. The acid also, to some extent,
destroys bacteria that are almost inevitably
swallowed with the food, but many escape
into the bowel. The gastric juice of young
mammals also contain rennin, a milk-curdling
enzyme. Thus the special action of the gastric
juice is on proteins.

50. The Intestine. The chyme is propelled
into the small intestine, which is of great
length; in it two processes occur: (1) the
completion of digestion, and (2) the absorp-
tion of digested matters. Near the beginning
of the small intestine, in the duodenum, two
fluids mix with the chyme, the bile, formed

INCOME OF MATTER 97

by the liver, and the pancreatic juice, secreted
by a gland similar in structure to the
salivary glands, called the pancreas. The
bile is constantly being formed by the liver,
and passes drop by drop from the end of the
bile-duct into the duodenum. This fluid
does not take an active part in the digestion
of the constituents of food, and it may be re-
garded more as an excretion or waste product
of the complicated chemical processes occur-
ring in the liver. Still, as it is poured
into the small bowel so near its beginning,
it must exert some influence. That influence
may or may not be beneficial according to its
quantity. If in great amount it may pass back
into the stomach and partly arrest the digestive
process there, as happens in a bilious attack ;
or it may to some extent interfere with
processes in the bowel if in excessive amount,
and it appears to act as a stimulant
to the musculo-nervous mechanism of the
bowel by which the chyme is propelled on-
wards. In excess it may cause diarrhoea.
A portion of the bile may be stored in the
gall bladder, an organ, however, that does not

98 PRINCIPLES OF PHYSIOLOGY

appear to be indispensable, as many animals
have no such reservoir.

Along with the bile from the liver, the
pancreatic fluid enters, often by a duct formed
by the confluence of the ducts of the two
glands This fluid is secreted only during
the digestive process, and the secretion appears
to be stimulated and modified in character
by a special enzyme in the duodenum called
secretin, a remarkable example of a ferment
body acting so as to excite the activity of
another enzyme-forming gland. Another
enzyme, known as entero-kinase, formed in
the duodenum, appears to facilitate the
action of one of the pancreatic ferments,
trypsin The pancreatic fluid is assumed
to contain three ferments : (1) one acting
on proteins and peptones, called trypsin,
splitting those up into simpler bodies,
mainly such as leucin and tyrosin (crystal-
lizable bodies) ; (2) another, amylopsin, acting
on the starch, cooked or raw, which has escaped
the saliva, changing it into grape sugar ; and
(8) one that acts on fats, lipase, splitting them
up into glycerine and a fatty acid, while the

INCOME OF MATTER 99

free acid immediately unites with alkalies in
the bowel, potash and soda, to form highly
soluble soaps. The pancreatic juice also con-
tains a milk-curdling ferment. The action on
proteins is to split up the protein molecule into
simpler soluble substances, such as leucin,
tyrosin, and simpler bodies known as amino-
acids. Some of the bodies so formed may be
absorbed into the blood, while any excess
is probably voided in the faeces.

51. The whole length of the small intestine
contains numerous glands, those in the duo-
denum termed the glands of Brunner, while
the others are known as Lieberkuhn's glands.
These glands secrete the intestinal juice,
which has a feeble action somewhat resem-
bling that of the pancreas. It contains a
special enzyme, erepsin. (See p. 76.) There
is also present an enzyme called invertase,
which splits up cane sugar into dextrose and
levulose.

52. The great intestine, which is much
shorter and wider than the small, may be
regarded as a receptacle for the refuse
materials of food stuffs that have not been

100 PRINCIPLES OF PHYSIOLOGY

digested, and for various substances excreted
by numerous tubular glands. The secretions
of the great bowel do not take an active part
in true digestion. Putrefactive processes also
are carried on, even in the small bowel, and
still more in the larger bowel, and these
processes, due to the activities of numerous
bacteria, still further split up the protein
molecules, with the production of offensive
smelling bodies, indol, skatol, phenol, etc.
These bodies, by uniting with sulphuric
acid arising from sulphates (originating from
the sulphur of proteins), form etherial sul-
phates, such as indoxyl-sulphate of potassium.
This body is called indican, and is voided
in the urine. Such fermentative and putrefac-
tive processes, all due to specific organisms,
also attack carbo-hydrates and fats, producing
lactic acid, butyric acid, sulphuretted hydro-
gen, carbonic acid, and other substances.
The absorption of these may cause a kind of
auto-poisoning of the individual.

53. It will be seen that all the constituents
of food are now soluble and ready for absorp-
tion, This is accomplished mainly in the

INCOME OF MATTER 101

small intestine, partly by the blood vessels,
and partly by special absorbents, the lacteals.
Covering the whole of the mucous membrane
of the small bowel there are innumerable
small finger-like processes, like the pile of
velvet. Each process is a little organ called
a villus. In the centre of each villus there is
a tube, the outer end of which communicates
with numerous minute channels ; this is the
commencement of the absorbent system. By
the confluence of the bases of these tubes a
network of fine tubes, running in the mesen-
tery (or web connecting the bowel with the
wall of the abdomen) is formed, and these
tubes, by confluence, form larger and larger
tubes until they reach certain gland-like
structures, the mesenteric glands. The ducts
of these glands, now called mesenteric lymph-
atic glands, pass to a special receptacle, the
receptaculum chyli, and from it a large
duct, the thoracic duct, runs up through
the thorax, and, at the root of the neck,
on the left side, opens obliquely into the
venous system, just at the confluence of
the internal jugular vein, carrying blood

102 PRINCIPLES OF PHYSIOLOGY

from the head and neck, with the superior
subclavian vein, coming from the left arm.
This lacteal system (so called because, during
the digestion of fat, it is filled with a milky
like fluid, the chyle) is the absorbent system
mainly for fats, taken up, either as a fine
emulsion or as soaps, from the bowel by the

54. In each villus, between its epithelial
covering and the centre, in addition to the
fine absorbents already noticed, there is a
rich plexus of capillary blood vessels. These
absorb all soluble matters, such as peptones,
sugars, possibly soaps, saline matters, water,
and any other substances in solution. The
blood thus circulating in the villi is gathered
up by veins, and these form the mesenteric
system of vessels. Blood is thus gathered
from all parts of the intestinal canal,
stomach, small intestine, and large intestine,
and by the vessels forming the portal system
and, by a large vein called the portal
vein, it is carried to the liver : It will thus
be seen that all the products of digestion,
except emulsive fats, and all soluble matters,

INCOME OF MATTER 103

are in the first instance carried to the liver.
In that organ, the largest gland in the body,
and the seat of intense physiological activities,
intricate chemical processes occur. One of
the results of these is the formation of bile,
which may be regarded as a waste product
arising from the chemical processes occurring
in the gland. The blood, laden with matters
absorbed from the alimentary canal, and
modified by the cells in the liver, issues from
the organ by the hepatic vein, which then
pours the blood into the venous system. The
matters thrown out in the bile will be con-
sidered in connection with excretion.

Thus it will be seen that all the matters
absorbed in the alimentary canal ultimately
reach the venous system. They all contribute
to the making of blood. The fatty matters
absorbed by the villi are modified by the
mesenteric glands. They feed the protoplasm
of these glands, which then gives off leuco-
cytes or colourless corpuscles. These glands
are abdominal lymphatic glands, and they
share with other lymphatic glands (found
in many parts of the body) in the

104 PRINCIPLES OF PHYSIOLOGY

production of leucocytes. Finally, matters
that are undigested ; chemical substances
arising from proteins that have not been
absorbed; special matters secreted by the
glands of the great intestine of which we know
little ; countless bacteria ; and earthy matters,
such as phosphates of lime and magnesia, —
are voided in the faeces,

55 There are several interesting questions
as to absorption that must be noticed, as an
answer to them takes us to first principles.
Water and soluble salts are absorbed un-
changed. The salts may be adsorbed. Carbo-
hydrates are all absorbed as sugars, and
they are carried to the liver and are there
transformed into glycogen (a kind of animal
starchy substance), and stored for a time
No doubt some may pass along in the
blood stream, and be at once used by the
tissues. It is highly probable that when
no fresh sugar is coming from the intestine
sugar is supplied from the liver to the
tissues, that is to say glycogen is changed
by a liver enzyme into sugar, and this is at
once washed away. There are good grounds

INCOME OF MATTER 105

for the view that leucocytes take some
part in these processes, as we find always a
great increase of these cells during absorp-
tion. Fat we have seen to be absorbed by
the lacteals of the villi. Ultimately the mole-
cules of fat reach the protoplasm in lymphatic
glands, and are there changed ; but probably
a portion of the fat is seized by special cells
in connective tissue (fat cells), and is stored
there in a liquid state. How it is used up by
the tissues is still obscure, but we may be
sure it contributes to the making of proto-
plasm in muscular, and more especially in
nervous, tissues.

It is also difficult fully to explain the
changes that happen in proteins. At one
time it was supposed that peptones were
absorbed as such, and thus entered the
portal circulation. This view has been
abandoned, and now it would appear that
protein matter is absorbed in simpler forms
than peptones, and especially as amino-
acids. These are acids belonging to the
group known to chemists as fatty acids,
substitution compounds in which one of the

106 PRINCIPLES OF PHYSIOLOGY

hydrogens of the radicle is replaced by a
molecule containing two atoms of hydrogen
and one of nitrogen. Thus take caproic acid,
one of the fatty acid series. It is represented
by the chemical formula C5HirCOOH;
substitute for one of Hn a group NH2, and
we have C5H10.NH2.COOH, or amino-
caprcic acid, a well-known body called
leucin. It is important to note that these
amino-acids, of which there is a large num-
ber known to chemists, are always among the
final products of the decomposition of proteins.
Hence it was inferred that proteins were ab-
sorbed as amino-acids. These, however, have
not been found in the blood, possibly owing
to great technical difficulties, and it is still
a matter undecided as to (1) whether proteins
are so absorbed, and (2) how and where they
are re-transformed into the proteins of the
blood. It is a fact, however, that they all
pass to the liver, and that during the absorp-
tion of proteins the nitrogen in the blood
increases.

Further, it would seem that protein matter
may be used up in two ways. A certain portion

INCOME OF MATTER 107

in the blood is carried to the tissues, and there
it is metabolized for the upbuilding of proto-
plasm. As we now know there are many
tissue-enzymes, it may be that in the living cell
these enzymes, in a sense, re-digest this portion
of proteid, changing it again into amino-acid
bodies, and that these are used for upbuilding
protoplasm. But there may be an excess of
protein, and it may then be thrown aside as
creatin and other bodies found in muscle-juice.
This portion we may call tissue-protein. Prob-
ably it has characters of its own different from
those of the other portion of the protein which
we must now consider. This second portion of
protein, which we may term excess-protein, is
decomposed by cells in the liver, passes prob-
ably through many stages and is ultimately
voided by the kidneys in the form of urea. A
rich protein diet always causes an increase in
the amount of urea eliminated. There are, how-
ever, critical objections to this view. Is this
complicated process merely an arrangement
for getting rid of excess of protein ? One
can hardly imagine this to be the case. At
present we are not yet in a position to state

108 PRINCIPLES OF PHYSIOLOGY

what occurs in a hepatic cell. The process may
not be a series of processes, — one having to do
with the storage of glycogen, another with the
making of substances in the bile, such as bile
pigments, bile salts, cholesterin, etc., — but one
synthesis and one decomposition.

CHAPTER VIII

THE BLOOD. ITS RELATION TO THE LIVING
TISSUES

56. WE have seen that the various food stuffs
rendered soluble by the processes of digestion
are taken into the blood. This fluid is brought
by the smaller vessels, the capillaries, into
close proximity to all the elements of the
living tissues. From the blood vessels a fluid
passes out through their walls and permeates
all the tissues, bathing their elements, so that
there is much truth in the aphorism that the
elements of the living tissues, and more especi-
ally the living cells, live like aquatic organ-
isms, that is to say, they live in a fluid, and
their lives and activities depend on inter-
changes between them and the fluid. This
fluid is the lymph. Some of it is used up in
the nutrition of the tissues, and the surplusage,
now containing in solution matters derived
109

110 PRINCIPLES OF PHYSIOLOGY

from the breaking up of substances in the
tissues — substances derived from their physio-
logical tear and wear — is carried off by a drain-
age system of tubes, the lymphatics. The
lymph, however, is not thrown out of the
body as useless, but, as in the economy of a
well-arranged manufactory, it is utilized ; it
is carried to lymphatic glands found
in many parts of the body and of the
same class as those already alluded to as
existing in the mesentery. By these glands
it is used up, elaborated, as is often
said, so as to nourish the protoplasm
of those organs, and it is ultimately
poured into the blood, either along with
the chyle in the thoracic duct, or by a
special duct, the lymphatic duct, which
joins the venous system at the root of
the neck on the right side. Thus the
blood receives all the lymph and all the
chyle. It also receives cellular elements
from the lymphatic glands, from the kind of
tissue called lymphoid or adenoid tissue,
found in many organs and beneath many
mucous membranes, and, in particular, from

THE BLOOD 111

the red marrow found in the cavities in the
bones. It also receives oxygen from the air
by the process of respiration. The blood also
receives matters that may be absorbed from
many surfaces, both internal and external,
such as the pleural and peritoneal cavities.
The blood is therefore a highly complex
fluid. It must be regarded not so much as
a fluid as a complex tissue, and as the physical
condition of its cellular constituents, the blood
corpuscles, as well as the nutrition of the tissues
to which it supplies lymph, depends on it,
we find that it varies very little either in its
physical characters or in its chemical constitu-
tion. Thus its specific gravity and its
viscosity vary within very narrow limits.
Matters coming to it by the channels above
indicated are constantly being used up by
the tissues ; so that, although a considerable
amount of these matters enters the blood daily,
the percentage amount of any one of them is,
as a rule, small. Again, matters that are waste
products — and which would be injurious to
living tissues, if they accumulated above a
small percentage — are continually being elimi-

112 PRINCIPLES OF PHYSIOLOGY

nated by various excreting organs. Thus
the blood does not vary much either in quantity
or quality, a physiological condition of great
importance.

57. As already mentioned, the blood is a
highly complex fluid. It contains three
kinds of corpuscles, (1) red corpuscles, or
erythrocytes, (2) white or colourless corpuscles,
(leucocytes), of which there are several varie-
ties ; and (3) minute particles called
blood plates. The red corpuscles, chiefly
concerned in respiratory exchanges, exist
in enormous numbers, — in human blood
amounting to as much as five million
in a drop of blood about one-twenty-
fifth of an inch in diameter. The white
cells probably perform several functions,
They may imbibe certain matters from
the fluid of the blood and elaborate these
into other substances. By their power of
spontaneous amoeboid movement they may
seize upon and digest worn out effete red cells,
or micro-organisms that in many diseases find
their way into the blood.

58. Recent observations on the blood,

THE BLOOD 113

mostly by way of experiment, have shown
that in the blood there are substances which
are of physiological importance although their
quantities may be so small as to be beyond
our present methods of analysis. These
bodies seem to act as chemical defensive agents
against disease. It is well known that the leu-
cocytes act as phagocytes, that is they seize,
hold, and devour bacteria and other micro-
organisms. But, in addition to this phago-
cytic action of leucocytes, the fluid of the blood
contains substances that are bactericidal.
These substances, probably protein in their
character, are destroyed by heating the blood
for an hour to 55° C. Possibly they are
derived from leucocytes. They may be called
bacterio-lysins. Other substances in the blood
may have the power of destroying red cor-
puscles. Thus the blood serum of one animal
has the power of dissolving the red corpuscles
of another species. Such bodies are called
haemolysins.

The importance of these bodies is now
generally recognized. Bacteria or bacilli of
many kinds, if they find entrance into the

114 PRINCIPLES OF PHYSIOLOGY

body, cause disease, either by multiplying in
enormous numbers or by producing substances,
called toxins, which act as poisons. A toxin
is probably of the nature of a protein or
proteose, and usually there is associated with
it another body, called an antitoxin, sad to
be of the nature of a globulin. Toxin and
antitoxin neutralize each other, so that a
mixture injected into an animal may produce
no effect. By a system of inoculating a
healthy horse with small but increasing doses
of the diphtheria virus, the serum of the
animal by and by contains a large amount of
antitoxin, and the injection of this serum in a
case of diphtheria may save life by neutralizing
the toxin of the disease. Sera prepared in this
way are now used in practical medicine with
beneficial effects. Further, they may confer
immunity, that is to say, the injection of such
fluids may protect against attacks of the
disease. Thus the body may be protected
against the invasion of specific organisms by
the phagocytic action of leucocytes, by the
globulicidal action of various substances in
the blood, and by the formation of antitoxin.

THE BLOOD 115

There may also be present in the blood sub-
stances called agglutininS) that arrest the
movements of bacteria and throw them
into masses or clumps, and in this con-
dition they are more readily devoured by
leucocytes. Lastly, there are substances
known as opsonins, that also appear to
increase the phagocytic power of leucocytes.
The true nature of these chemical sub-
stances is unknown. They are probably
proteins, but whether they are different
substances or modifications of one substance
s a question to be answered by further re-
search. The history of this obscure subject
is a striking illustration of the complexity
of the physiological processes that may
possibly occur in the blood.

59. The blood is rich in proteins, especially
in the form of a variety of albumen and of a
protein substance known as serum globulin
or fibrinogen. It contains traces of many
other substances. If we examine the blood
as it circulates in the capillaries, under
the microscope, we see that the fluid, liquor
sanguinis, is an almost colourless fluid, and

116 PRINCIPLES OF PHYSIOLOGY

that the corpuscles, in single file, are
carried along by the stream. When shed,
however, it quickly coagulates, that is it
clots, and the clot, in a suitable vessel, is
soon surrounded by and floats in a serum.
This power of clotting no doubt is a salutary
function, as when vessels have been accident-
ally cut, they are, as a rule, soon plugged by
the clot, and bleeding ceases. Much investi-
gation has been expended on the phenomenon
of clotting, a process somewhat analogous to
the clotting of milk when it sours, from the
formation of lactic acid, or when acted on by
the ferment of rennet. The milk separates into
curd and whey ; the blood separates into serum
and clot. A clot consists of blood corpuscles
and a substance called fibrin. If we place
a piece of blood clot under a water tap, we can
wash out the corpuscles and we obtain fibrin
in the form of a yellowish fibrous material.
It is evident that the formation of fibrin, which
entangles the corpuscles in its fibrous meshes,
produces a blood clot. There is, however, no fib-
rin in blood, but a substance called fibrinogen.
The theory at present in vogue is that when

THE BLOOD 117

blood is shed there is at once the death of
many colourless cells. These contain a pro-
tein called pro-thrombin, which, in turn,
produces an enzyme known as thrombin, and
this ferment, in association with salts of lime,
converts fibrinogen into fibrin. To account
for the fact that blood rarely clots in living
vessels, we may assume the existence of a
body produced by the living cells lining the
vessels which prevents thrombin from acting
(an anti- thrombin). There is still uncertainty
as to what precisely happens in the remark-
able phenomenon of the clotting of blood,
and there is little doubt that if it were
thoroughly understood, light would be thrown
on other physiological phenomena, as it may
be taken as the type of a certain class of
changes in living matter.

60. The blood is not only a nutritional
medium but it is also intimately connected
with respiration. The red cells, by the action
of the pigment they contain, known as
haemoglobin, are engaged in carrying oxygen
to the tissues and also it would appear to
some extent in the carrying of carbonic acid

118 PRINCIPLES OF PHYSIOLOGY

from the tissues to the lungs, there to be
eliminated.

61. In order that the blood may be
brought into close proximity to the tissues,
we find a system of tubes, the organs of the
circulation, known as arteries, capillaries, and
veins, and at one point of the circulation,
where the arteries begin and the veins ter-
minate, we find a contractile force-pump, the
heart The walls of the arteries near the heart
are thick, strong, and highly elastic ; in those
farther away we find the elastic wall gradually
becoming thinner, and a contractile wall of
non-striated muscle appears, and becomes
thicker as we pass onwards, until in the smaller
arteries, or arterioles, the muscular coat is
the most pronounced. The arteries terminate
in the capillaries, which form a network of
minute tubes, many having a diameter of not
more than the three-thousandth of an inch.
These capillary networks bring the blood
close to the living tissue elements. Some
tissues, and always those in which there is
great physiological activity, are more vascular
than others. The capillaries terminate in the

THE BLOOD 119

veins, thin walled vessels, which carry the
blood back to the heart. The smaller veins,
by their confluence, form larger and larger
veins, and the large veins, in various situations,
are furnished with valves which, when open,
are directed towards the heart, and thus direct
the flow of blood to that organ. The heart
itself, in man, has four cavities, two auricles,
a right and left, that receive blood, and
two ventricles, right and left, that drive
the blood out. The right auricle receives
the blood from the peripheral parts of the
body, and the left receives it from the
lungs. The two auricles contract simul-
taneously. The two ventricles then simul-
taneously contract, the right driving the
blood through the pulmonary circulation —
arteries, pulmonary capillaries, veins — to the
lungs, for respiratory purposes, while the left
ventricle drives the blood through the
systemic circulation, — arteries, capillaries, and
veins, — through the body, so as to bring the
highly oxygenated and nutritious blood to
the tissues. Valves are placed at various
orifices of the heart and they so work

120 PRINCIPLES OF PHYSIOLOGY

that the blood must flow in the required
direction.

62. The hydraulic principles of the circu-
lation are remarkable. Blood must flow from
situations of higher pressure to situations of
lower pressure. High pressure is kept up in
the great arteries by the contractile action of
the left ventricle of the heart acting like a
force pump and, with each stroke of contrac-
tion, throwing blood into them, so that, in a
sense, they are over-distended. During the
intervals between the heart beats, the walls
of the arteries recover themselves by the
resiliency of their elastic coats. This disten-
sion and elastic recoil constitutes the pulse,
which is a wave of motion along the walls of
the arteries, starting from the heart, travel-
ling onwards with a certain velocity, and
becoming smaller and smaller until there is
no pulse in the smallest vessels, the capil-
laries. In consequence also of the loss of
energy by friction, and by the distension of
the arterial coats, the movement of the blood
becomes slower and slower until, in the capil-
laries, the blood is slowly meandering onwards

THE BLOOD 121

at a very low pressure. This is exactly the
condition most favourable for the transuda-
tion of fluid through the thin walls of the
capillaries for the nourishment of the living
tissues. But there is another remarkable
arrangement that suits two purposes : the
muscular wralls of the arterioles, by contracting,
can vary the diameter of these small vessels.
When the calibre is diminished, it will be
evident that the blood will not pass through
the small vessels so easily as it will do when
the calibre is increased. The contractile
arterioles act like a kind of stop-cock at one
part of the system. When the stop-cock is
open, as when the arterioles are dilated,
the blood flows through easily, the arterial
system empties quickly through the capillaries
into the veins, and the pressure in the greater
arteries falls. When the stop-cock is partly
closed, the blood will meet with resistance,
and the pressure in the larger arteries rises.
Thus, as the arterioles are always partially
contracted under the influence of special
nerves, there is always a sufficiently high
pressure in the arterial system to keep up the

122 PRINCIPLES OF PHYSIOLOGY

supply of blood to the capillary districts even
between the heart beats. When the heart
ceases to beat, as at death, the arterioles
become at the same time widely dilated, the
pulse disappears, and by the elastic recoil of
the walls of the great arteries the blood
passes through the capillaries into the veins.
Hence, after death, in ordinary circumstances,
the blood is found in the veins, while the
heart and arteries are empty It will be
seen, also, that the contractile coat of the
arteries regulates the supply of blood to various
capillary districts, according to their physio-
logical necessities.

63. The movements of respiration also
assist the circulation. During inspiration,
when the chest is dilated, pressure is removed
from the surface of the heart and of the great
vessels springing from it ; these tend to dilate
and thus the blood is as it were sucked towards
the heart by the great veins and by the
right auricle and right ventricle. During
expiration there is increased pressure on the
heart, more especially when expiration is
forced, and the blood does not flow towards

THE BLOOD 123

the heart so easily. The flow of blood
towards the heart is also favoured by muscular
movements in the limbs pressing on the thin
walled veins, and as these are provided with
valves opening towards the heart, the blood
must flow onwards. Pressure on the veins
of the organs in the abdomen must also assist,
and so great is the capacity of the circulatory
system in the abdominal and pelvic cavities
that a quantity of blood equal to all the blood
in the body might be therein contained. If
there is more blood in one part of the body
there will be less in another. An adjustment
of local circulations is constantly going on,
according to the degree of physiological
activity of one organ or another. If there is
a large supply of blood to the abdominal
viscera, as during digestion, or to the skin,
as when exposed to heat, there will be less
blood in other internal organs. This may in
part account for the mental lethargy after a
full meal, and for the lassitude one feels
during hot weather.

64. The circulation of the blood is thus
carried on in accordance with the physical laws

124 PRINCIPLES OF PHYSIOLOGY

of hydraulics. We might imitate it roughly
by elastic tubes and a force pump. We can
drive water through the streets and houses
of a town by a head of water or a powerful
engine, but even with our present technical
skill, we could not automatically regulate the
supply according to the wants of different
districts by using automatically working
elastic and contractile pipes.

CHAPTER IX

THE OUTPUT OF WASTE MATTER

65. IT has already been pointed out that the
activities of the living tissues cause to some
extent a breaking up of living matter, and the
appearance of waste products. In addition
to this, waste matters may arise from the
using up by the protoplasm in cells of matters
previously stored up in them. That is to
say, there may be intracellular chemical
changes excited by enzymes in stored matters,
as well as chemical changes involving the
protoplasm. Both of these varieties of chemi-
cal change may produce substances that are
of no further use in the body, and may even
be injurious if allowed to accumulate in the
blood. ' Such matters are not allowed to
accumulate : they are quickly removed so
that only small percentages are usually found
in the blood, and this fluid, as has already
125

126 PRINCIPLES OF PHYSIOLOGY

been explained, is maintained in a state of
nutritive equilibrium. The separation and
elimination of waste matters are effected by
the process termed excretion. A secretion,
such as saliva, or gastric juice, is a fluid
holding matters in solution which have been
formed by the activities of the cells in secreting
glands, and it is intended to be used for some
other purpose in the economy of the living
body. Reference has already been made to
the uses of the saliva and of the gastric juice.
An excretion, on the other hand, is the separa-
tion from the body of such a fluid as urine
by the kidneys, or bile by the liver-fluids of
no further use. The chief excretive mechan-
isms will now be considered.

66. Lungs. By the process of respiration,
carbonic acid is excreted by the lungs. This
substance, carbonic acid, is produced in
connection with the activities of all living
matter. It is formed in the tissues, especi-
ally in the glandular, nervous and muscular
tissues ; it is abundant in lymph ; it exists
in the blood in a state of loose chemico-physi-
cal combination with the potassium salts and

OUTPUT OF WASTE MATTER 127

with the haemoglobin of the red cells. The
lymph surrounding the living tissues is, as
already explained, a respiratory as well as a
nutritive medium. The living elements, in a
sense, breathe in the lymph. They receive
oxygen from it and they give up oxygen to it.
The tension of the oxygen in lymph is high,
whereas that of carbonic acid is low, as it
is quickly removed. This facilitates the
interchange of gases, which we may regard
as an internal respiration. The lymph ulti-
mately reaches the blood and carries the
carbonic acid with it. Further, in the tissues
themselves there is an absorption of carbonic
acid by the small capillaries and veins. The
blood thus becomes venous. It is carried
away to the right side of the heart by the
veins, from thence it passes by the pulmonary
circulation to the lungs, and there the carbonic
acid is got rid of into the air cells of the lungs,
and, finally, it reaches the outer air in the
air of expiration. How the carbonic acid
passes out of the capillaries into the air cells
has not yet been clearly made out. The
tension of the carbonic acid in venous blood is

128 PRINCIPLES OF PHYSIOLOGY

greater than the tension of the gas in the air
cells of the lung, and it may be supposed that
this tension would drive off the carbonic acid.
Still there are difficulties with regard to this
purely physical explanation, and it may be
that the cells found on the delicate wall
between the blood and the air may exert
selective action, and, in a manner analo-
gous to true secretion, excrete the carbonic
acid.

67. Respiration, however, is a double
function. Not only is carbonic acid eliminated
in the air cells of the lung, but oxygen is
absorbed into the blood, and by the blood
it is carried to the tissues. There can be no
doubt the oxygen is taken up by the all
important constituent of the red cells called
haemoglobin. It combines to form a loose
union with this pigment, The red corpuscles,
laden with oxygen, are hurried to the tissues,
and there a reverse process occurs. The
oxygen leaves the oxy-haemoglobin probably
in successive small quantities, passes into
the lymph, and is at once taken up by
the living tissues. In the air cells of the

OUTPUT OF WASTE MATTER 129

lung the oxygen passes through the thin
wall between the blood and the air possibly
physically, inasmuch as the tension of the
oxygen in the air cells, especially at the
end of an inspiration, is greater than the
tension of the oxygen in the blood, — but again
various considerations lead us to suppose that
the taking up of oxygen may be a vital
process due to the activity of the cells lining
the air cells and also lining the vessels. The
air bladder of a fish is the representative of the
lung ; in many cases it contains a large
percentage of oxygen, secreted from the
blood of the fish by the epithelium lining
the bladder. (It is remarkable, however,
that in shallow water fishes the gas in the
air bladder is chiefly nitrogen.) This oxygen
was in the first instance separated from the
water by the blood vessels of the gills as the
water flowed over them. In the tissues,
again, internal respiration may not be entirely
a physical process, as we are dealing with
living tissues. Here, again, there may be
selection of living gases by living cells.
What we usually think of as respiration

180 PRINCIPLES OF PHYSIOLOGY

is a series of muscular movements by which
the chest expands, as in inspiration, and
the air rushes into the upper air passages
to mix with the air already there : this
is followed in ordinary expiration by an
elastic recoil of the chest wall by which the
air is expelled from the upper air passages.
The air in those passages mixes with the air
in the ultimate air cells by a physical process
of diffusion of gases. The whole of this process,
the distension and recoil of both chest wall
and lungs, constitutes a pulmonary ventilation.
The essential phenomena of respiration are,
however, in the air cells and in the tissues.
The lungs may eliminate a small amount of
water by evaporation from the respiratory
gases, and, occasionally, other matters
may pass off which taint the breath. The
mechanism of external breathing is carried
on by a complex system of muscles and by a
special innervation.

68. Kidneys. Excretion is also carried on
by the kidneys. These organs, which may be
regarded as highly modified tubular glands,
separate from the blood, water ; various

OUTPUT OF WASTE MATTER 131

saline matters, chiefly chloride of sodium
(common salt) and phosphates of the alkalies
(potash and soda), and of the alkaline earths
(lime and magnesia) ; various nitrogenous
substances, more especially urea, uric acid,
creatinin, etc. ; and pigmentary matter.
The kidneys also take a slight part in the
elimination of carbonic acid. These matters
are separated from the blood mainly by the
activity of the epithelial cells lining the
uriniferous tubules. In the cortical part of
the kidney there are remarkable structures
known as the Malpighian Bodies, consisting
of a glomerulus or ball formed by a network
of capillaries, surrounded by the dilated end
of a uriniferous tubule, so as to form a capsule
lined by a peculiar form of epithelium. The
end of the tubule is infolded over the capillary
nodule so that a double wall surrounds the
nodule. Thus a somewhat complex membrane
is formed like a kind of cap, and three layers,
blended together, separate the blood from the
urine — namely, the wall of the capillaries and
a double wall formed by the infolded end of
the tubule. This was once supposed to

132 PRINCIPLES OF PHYSIOLOGY

orm a filtration apparatus by which the
watery constituent of the urine, holding salts
and other matters in solution, was filtered
from the blood through the thin membrane

nto the end of the tubule It would appear,
however, that the process is not one of simple
physical filtration, but that there is a selective
action due to the vital activity of the epithe-
lium. A minute vessel passes from the
glomerulus or ball of capillaries, and this
divides again into capillaries which ramify
on the first portion of the uriniferous tubule.
The epithelium in this portion is of a peculiar
kind, and it has been thought that it has to
do with the separation from the blood of nitro-
genous matters. There is still considerable
obscurity as to the precise mechanism by
which urine is formed.

69. In a healthy man about fifty ounces are
excreted daily. Its colour is due to a mixture
of pigments, chiefly urochrome and a small
amount of urobilin. The reaction to test-paper
is acid, due chiefly to the presence of the acid
phosphate of soda. The origin and destination
of the nitrogenous constituents require special

OUTPUT OF WASTE MATTER 133

notice, more especially as illustrating the
modes of excretion. It is evident that
nitrogenous waste matters should be soluble
so that they may be carried off in the urine
Urea, of which about five hundred grains are
eliminated daily, is readily soluble in water
It is a carb-amide, and is represented by the
formula CO(NH2). It contains the same ele-
ments as cyanate of ammonia, but it has not
the same molecular structure. Under the influ-
ence of various enzymes, it takes up water,
and is changed into ammonium carbonate,
which gives the ammoniacal odour to decom-
posing urine. In such urine we always have a
precipitate of phosphates of lime, phosphate of
magnesia, and the ammoniaco-magnesian, or
triple, phosphate, as these are not soluble in an
alkaline fluid. As already pointed out, a large
proportion if not the whole of the urea is
formed in the liver by the splitting up of pro-
tein matter that has come from the intestine,
and, to be more precise, it is formed from
amino-acids. This is sometimes spoken of as
the exogenous formation of urea. Along with
urea we always find traces of ammonia.

134 PRINCIPLES OF PHYSIOLOGY

One of the substances produced by the
decomposition of muscle-protoplasm is a
nitrogenous body called creatine. By union
with the elements of water, it splits into urea
and sarcosine, showing a relationship to the
former substance, and possibly part of it
may ultimately be converted into urea, as it
does not appear normally in urine. A
closely allied substance, differing from
creatine as regards its formula by the loss
of the elements of water, is creatinine,
which always exists in urine. It is in all
probability formed, not from the creatine
of muscle, as was once supposed, but from
the metabolism of protein in the liver,
and as it is poisonous it is thrown out in the
urine. There is still obscurity on this point.
Another nitrogenous waste product in the
urine is uric acid, of which from seven to ten
grains are separated daily. Unlike urea, it is
highly insoluble, but being an acid it unites
with the alkalies, soda and potash, to form
urates, which are highly soluble, and in this
form it is thrown out. If in excess, or if there
is not sufficient base to unite with it, uric acid

OUTPUT OF WASTE MATTER 135

may appear in various crystalline forms in
the urine, and when this habitually occurs,
various symptoms of illness may appear
which are spoken of as gouty or rheumatic.
There can be no doubt that uric acid is derived
from the breaking down, not of cell-substance,
but from the oxidation of nuclein, one of the
chief chemical substances in the nuclei of
cells. This shows that even nuclei, on which
the activity of cell-life so much depends, are
the seat of metabolic changes, and that
there are processes of breaking down. It is
known that nuclein yields, during certain
chemical reactions, a chain of nitrogenous
bodies, all more or less closely related, known
as the purine bases. These are purine,
hypoxanthin, xanthin, adenin, guanin, and
uric acid. They sometimes appear in the
urine and they abound in such tissues as
are the seat of active metabolism. Certain
foods, such as liver and sweetbread, contain
these substances. These bases may thus be
formed exogenously from food stuffs or endo-
genously by the metabolism of tissue. Any
increased activity in nuclei, implying tear

136 PRINCIPLES OF PHYSIOLOGY

and wear, is shown by the appearance of
these bodies.

We have only recently had a glimpse into
the transformations by which members of
this series, ending in uric acid, are formed.
This is done by the activity of various enzymes
found in the tissues. These have been
extracted and their chemical activities studied,
.and there can be little doubt that each of these
nucleo-zymases takes its share in the work.
Some may bring oxygen into play (oxidases),
while others effect specific chemical changes.
It would seem that in the liver there also
may be an enzyme which breaks up uric acid
itself. The ultimate result of these remark-
able changes is that substances arising from
the breaking up of nuclei are gradually trans-
formed into uric acid, which (as urates) is
-eliminated in a soluble form. Finally, a
substance known as hippuric acid is elim-
inated in small amounts in the urine. It
abounds in the urine of herbivora, arising from
substances in the food of such animals, and be-
longing to the benzoic acid series. If benzoic
acid is given to a man, it unites with glycine

OUTPUT OF WASTE MATTER 137

in the liver, with the separation of the
elements of water; hippuric acid is thus
ormed and appears in the urine. This is a
striking example of a synthesis in the living
body.

70. Another organ by which excretion is
effected is the skin This structure not only
has a protective function, as it covers the
whole surface of the body, but it has also an
excretory function. Carbonic acid is to a
small extent eliminated. The sweat, consist-
ing of water holding a small amount of salts
in solution (chiefly chloride of sodium, and
phosphates), is separated by numerous long
tubular glands, the sweat or sudoriparous
glands, lined with epithelium. This fluid, at
certain temperatures, may at once pass into
a state of vapour or gas, thus taking up heat,
and cooling the surface, or, as in profuse
sweating, it may appear as sensible drops on
the surface of the skin. A kind of oily
matter is secreted by another set of glands
in the skin, the sebaceous glands, which some-
times open by ducts on the surface, or into the
little pouches from which hairs spring.

138 PRINCIPLES OF PHYSIOLOGY

Sebaceous matter contains, in addition to
water and a very small amount of salts,
various fatty acid substances. The sebaceous
matter lubricates the surface of the skin.
The skin, however, has other important
functions. It is not only the organ by which
variations of temperature are experienced,
but it has to do with the regulation of the
temperature of the body. This will be noted
in connection with animal heat. It is also
the seat of various sensory mechanisms con-
nected with the sense of touch.

71. Matters are also excreted from the
body by the bowel. These consist of the
refuse materials of food which have never
really entered the tissues of the body, and
which are therefore not true excretions.
Along with these there are bodies derived
from the bile, such as pigments, etc., and
the secretions of the numerous mucous glands
found throughout the whole length of the
bowel, and more especially in the great
bowel. Little is known of the chemical
nature of those matters, nor of the exact
origin of the large amount of saline

OUTPUT OF WASTE MATTER 139

matters, chiefly phosphates, found in the
faeces. Finally a large portion of dried
faecal matters consists of bacteria, which
have already been referred to as existing
in enormous numbers in the alimentary
canal.

72. There is still another organ which, from
one point of view, may be regarded as excre-
tory, namely the liver. A portion of the bile
is undoubtedly thrown out in the faeces, but
others matters are re-absorbed and return to
the liver. This organ is the seat of numerous
chemical and vital processes that are in a
sense hidden. These will be further con-
sidered.

73. The bile is an alkaline fluid containing
usually a large amount of a mucus-like matter,
which gives it a peculiar " ropy " character
when poured from one vessel into another. It
contains two nitrogenous pigments, bilirubin
and biliverdin. In the bowel bilirubin is
robbed of oxygen by reduction processes and
becomes the pigment of the faeces, stercobilin.
Part of the latter may be re-absorbed, and is
then eliminated in the urine as urobilin, one

140 PRINCIPLES OF PHYSIOLOGY

of the pigments of the urine. The origin of
these pigments is undoubtedly the decom-
position of the haemoglobin of effete or
worn out red blood corpuscles. Where the
haemoglobin is set free and decomposed is
doubtful. This probably occurs both in the
spleen and in the liver. It is important to
note that all the blood that has passed through
the spleen goes to the liver. The relation of
bilirubin to the blood pigment is undoubted,
as haemoglobin is a compound of haema-
tin, containing the all-important iron, and a
globulin. If the iron is removed from haematin
we have a body called haematoidin, or iron-free
haematin, produced. This is identical with
bilirubin. Thus we see the steps of the pro-
cess for the elimination of waste pigmentary
matters

74. The bile contains the sodium salts of
highly complicated acids, known as the
bile acids, forming glycocholate and tauro-
cholate of sodium. The first is the more
abundant in human bile. Both contain
nitrogen ; taurocholic acid alone contains
sulphur. Each may be split up into (a) an

OUTPUT OF WASTE MATTER 141

acid, cholalic acid, associated with glycin in
glycocholic and with taurin in taurocholie
acid. Both the origin and the ultimate fate
of the bile salts are in obscurity. As they both
contain nitrogen, and one contains sulphur,
we must look for their origin in protein
metabolism, but we know nothing of the steps
of the process. In the bile (in human bile
glycocholate of soda forms the chief part of
the solids) they reach the intestine. We are
not aware of any special function fulfilled by
them in connection with either intestinal
digestion or intestinal absorption. Only a
very small amount of the bile salts appears
in the faeces. It follows that they must be
re-absorbed and carried back to the liver by
the portal circulation and again eliminated
in the bile. Thus a kind of bile-salt circula-
tion has been imagined, but there is no hint
as to any use of this arrangement. Traces
of substances may appear in the urine that
may have originated from chemical changes
in the bile salts. Lastly, small quantities of
cholesterin or cholesterol may be found in bile.
It forms the chief constituent of gall-stones,

142 PRINCIPLES OF PHYSIOLOGY

concretions formed in the bile ducts and in the
gall bladder The origin of this substance is
still imperfectly known, but it is formed from
metabolism of tissue. It is present in all cells,
and when these are broken down, it is not
thrown out as a waste product, but is used up
to form new cells. Thus, red blood corpuscles
are disintegrated in the liver and cholesterin
appears in the bile. It is then re-absorbed,
probably with other substances, and is carried
to the tissues to form new cells. This is a
striking example of physiological economy.

75. By those various processes of excretion
waste matters and injurious matters are
removed from the blood, as has already been
explained. This fluid is therefore maintained
in a condition of physiological equilibrium,
and this is more remarkable when we consider
that it is constantly the seat of exchanges.
It is almost momentarily receiving matters
on the one hand and giving them up on the
other. In a sense, everything removed from
the blood must more or less alter its quality.
From this point of view the growth and
development of the epidermic cells on the

OUTPUT OF WASTE MATTER 143

surface of the skin, and which are constantly
being shed from the surface in myriads, the
growth and development of all epidermic
appendages, such as hairs, nails, horn, feathers,
etc., remove certain matters from the blood
and alter its quality. We may indeed go
farther and say that the development and
growth of all tissues, as they depend on matters
taken from the blood, must alter that fluid
Thus we may understand that the abnormal
development of any tissue or organ must have
a similar effect, and in some such way the
nutrition of one organ must affect that of the
others.

CHAPTER X

HIDDEN PROCESSES AND ULTIMATE PHENO-
MENA OF NUTRITION

76. THERE are not a few processes occurring
in the body which are so hidden as not to be
at all evident to a superficial examination ;
and yet they are of the highest importance.
Several examples of these may now be referred
to. First, we will consider what is usually
called the glycogenic function of the liver.
This organ, the largest gland-like structure in
the body, consists of myriads of cells, the
hepatic cells, and it is more richly supplied
with capillary blood vessels than any other
structure in the body. It receives two kinds
of blood, red arterial blood from the systemic
circulation by the hepatic artery, and blood
more like venous blood, often laden with
matters derived from the alimentary canal —
portal blood — by the portal vein. The blood,

144

HIDDEN PROCESSES 145

after circulating through the liver, is carried
off by a single vein, the hepatic vein, which
pours it into the systemic venous circulation.
There it mixes with other venous blood,
reaches the right side of the heart, passes to
the lungs (pulmonary circulation), is sent on to
the left side of the heart, and is then propelled
by the systemic circulation to all parts of the
body. Thus, as already mentioned, the whole
of the blood that has circulated through the
alimentary canal passes through the liver
before it reaches the general venous system.
This is the portal circulation. In the cells o!
the liver very active metabolic changes take
place, new substances are formed, complex
bodies are split up, possibly red corpuscles are
decomposed, and as the result of all this, we
have bile formed, which, as already seen,
passes into the first portion of the small bowel,
the duodenum. The formation of bile was at
one time regarded as the proper function of the
liver. But it is now known that this is not
the case. The bile is only a by-product led
off from this remarkable manufactory.

77. As already pointed out, the blood with

146 PRINCIPLES OF PHYSIOLOGY

which the liver is supplied by the portal
system contains during the digestive and
absorptive processes large amounts of pro-
teid and of carbo-hydrate in the form of
grape sugar. What happens to the proteid
has already been discussed (p. 66). A portion
of it, however, may be decomposed into a
nitrogenous and a non-nitrogenous portion.
The nitrogenous portion may, by synthesis,
assist in the formation of other molecules of
proteid or of certain bodies found in the liver,
such as the complicated bile acids which,
united to soda to form the bile salts, appear in
the bile (p. 140). In the chemical changes
affecting the nitrogenous portion one of the
bodies formed is undoubtedly urea (p. 132).
This substance often represents an excess of
proteid in the diet ; at all events a meal rich
in proteid is followed by an increased forma-
tion of urea. The urea is washed out of the
liver by the blood, but as it is quickly removed
by the kidneys, it appears in the urine, and
the percentage amount in the blood is always
small. On the other hand, the non-nitro-
genous residue of the proteid may apparently

HIDDEN PROCESSES U7

be transformed into a carbo-hydrate, and it
may be one of the sources of the distinguishing
carbo-hydrate in the liver known as glycogen.
78. The chief source of glycogen, however,
is undoubtedly grape sugar that has arrived
in the portal blood from the alimentary
canal. Glycogen is a non-nitrogenous body
much resembling starch, indeed it may be
regarded as an animal starch. After a period
of digestion and absorption, it is found in
the form of minute granules in the interior
of many hepatic cells. For a time it is stored
in these cells, so that the liver is a storehouse
of carbo-hydrate. It is interesting to note
that in digestion, as we have seen, all
carbo-hydrate is transformed into grape sugar,
while in the liver we find the process reversed
and a kind of starch, glycogen, is again formed
from grape sugar. The first transformation
is accomplished by various enzymes, while the
second is effected by the living hepatic cells,
or possibly by an enzyme in the cells While
absorption is going on, a certain amount of
grape sugar passes through the liver un-
changed, and is carried to the muscles, where

148 PRINCIPLES OF PHYSIOLOGY

it is used up in the chemical processes occur-
ring in that tissue connected with contraction.
During the intervals between absorptive
periods, and while no carbo-hydrate is derived
from the bowel, the muscles still require
carbo-hydrate, and this they obtain from the
store of glycogen stored in the hepatic cells.
How the glycogen is removed from the cells,
and again re-transformed into sugar, either
in the hepatic cells, or in the colourless cor-
puscles, or in the muscular tissues themselves,
has not yet been clearly explained. Probably
again enzyme action is called into play.
Another enzyme has been found in the liver,
capable of transforming the glycogen into
sugar, and various sugar-forming substances
have been found in muscle. There appears to
be in muscle, especially at an early stage
of development, a variety of glycogen, or
carbo-hydrate destined for its nutrition. The
phenomena that occur in the hepatic cell
are unknown. It is possible, as already sug-
gested, that the transformations in protein
matter, as well as in carbo-hydrate matter,
may be one intricate chemical operation — a

HIDDEN PROCESSES 149

series of decompositions succeeded by syn-
theses— one result of which is the throwing
out of useless residues that are found in
some of the constituents of the bile. The
glycogenic function gives us only a glimpse
into the nature of the complex chemical
phenomena occurring in a hepatic cell. In
the liver also there appears to be a destruction
of effete red blood corpuscles with the decom-
position of haemoglobin, and the excretion in
the bile of pigments and of cholesterol.

79. In recent years a remarkable discovery
has been made with regard to certain organs
that were previously a puzzle to physiologists,
such organs as the thyroid body or gland
found in front of the upper end of the trachea
or windpipe ; the two suprarenal bodies found
immediately above the upper end of each
kidney ; the pituitary body found at the base of
the brain ; the spleen, lying on the left side of
the stomach ; and various organs now known
to belong to the lymphatic system, such as
the lymphatic glands, the tonsils, and the
Peyerian glands found in the small intestine,
more especially in its third and lower portion,

150 PRINCIPLES OF PHYSIOLOGY

the ileum. These organs all agree anatomi-
cally in having no duct Hence, they are
sometimes called the ductless glands. It is a
misnomer to call them glands, as they are not
in any sense true glands, and they would be
more aptly designated " body " or " bodies."
All those organs that belong to the lymphatic
system proper contain a peculiar kind of
tissue, known as lymphoid tissue (found also
in the marrow of bone and below mucous
surfaces), consisting of a network of fine
fibres, with small masses of protoplasm at the
junctions of the fibres, as if the tissue were
formed of star-shaped cells, the rays of which
unite or anastomose to form a network. These
lymphatic bodies are concerned in the develop-
ment and growth of colourless cells of the
blood, but it is probable they have other
hidden functions at present unknown.

80. The other bodies above mentioned are
now known to form what have been termed
internal secretions, which have important
physiological effects. Thus the thyroid body
forms a chemical substance, now known as
thyroidin, which contains iodine, and which

HIDDEN PROCESSES 151

seems to have the property of destroying
mucinoid material, probably absorbed, in a
more or less modified condition, from mucous
surfaces. At all events atrophy of the thyroid
body produces a peculiar disease known as
myxoedema, in which the cellular tissues are
infiltrated with a mucinoid matter, while there
are symptoms of an anaemia (deficiency of red
cells of the blood). This condition is much
modified or disappears on administering raw
thyroid, powdered thyroid, or the thyroidin
extracted from the organ of the sheep or
similar mammal. As curious nervous symp-
toms appear after removal of the thyroid it
may have other internal functions.

81. The suprarenal bodies were at one time
thought to have to do with the formation
or modification of pigment, and possibly this
may be the case, but they are now known to
produce a chemical substance termed adrena-
lin, which has a specific action in stimulating
non-striated muscular fibre. Thus it stimu-
lates the coats of the arterioles, causing
their calibre to be very much diminished,
and as the heart still vigorously beats, the

152 PRINCIPLES OF PHYSIOLOGY

pressure of the blood in the great vessels is
much increased, a condition, within limits,
favourable to a vigorous circulation. Adrena-
lin is now used medicinally, as a powerful
styptic by which bleedings may be arrested.
This is a striking example of a so-called internal
secretion.

82. Similarly the pituitary body appears to
exert an influence on the growth and develop-
ment of bone, and morbid conditions of the
organ are apparently related to a curious
disease called acromegaly, in which the bones
of the face and fingers in particular become
enormously developed. This subject, how-
ever, is still obscure.

83. Another organ which is the seat of
many hidden processes is the spleen. It is
the largest of the ductless glands. It has
a strong fibrous capsule, and passing from
the capsule in all directions into the interior
of the organ we find septa or partitions of
connective tissue and unstriated muscle,
dividing the organ into numerous compart-
ments. These are filled with spleen pulp.
This pulp consists of finer fibres forming a

HIDDEN PROCESSES 153

kind of network, in the meshes of which are
numerous granular corpuscles like those found
in lymph. There are also numerous red
corpuscles and also cell-like bodies enclosing
red corpuscles or pigmentary matter. The
splenic artery which brings blood to the spleen
divides into branches like the twigs of a tree ;
there are no capillaries; the blood infiltrates
the pulp ; and from the spaces in which the
pulp lies veins originate which, by confluence,
form the splenic vein. The blood of the splenic
vein, as already mentioned, passes to the
liver (p. 140). The spleen has also curious little
masses of lymphoid tissue, called Malpighian
corpuscles, which are closely connected with
the branching vessels. The chief function of
the spleen is the formation of colourless blood
corpuscles, especially by the lymphoid tissue in
the Malpighian bodies. The blood of the splenic
vein is always rich in white corpuscles. There
is little doubt also that disintegration of effete
corpuscles occurs in the spleen, and from
these chemical substances are formed like
those originating in nitrogenous metabolism,
such as those of the uric acid series (p. 135).

154 PRINCIPLES OF PHYSIOLOGY

Curious rhythmical movements of the spleen
have been studied, and on a tracing of these
movements large waves occur about once in a
minute ; on these there are smaller waves due
to respiratory movements ; and on these, again,
still smaller waves, corresponding to the beats
of the heart. This rhythmic mechanism
must assist in the transmission of blood
through the organ. It is influenced by special
nerves.

84. The ihymus gland, found in the chest
behind the breastbone, is a blood gland of
later foetal and early infantile life. Very
little is known of its functions.

85. It is suspected that other organs,
having definite functions with which we are
acquainted, have also hidden functions little
understood. In this way the kidneys may
have a hidden function ; at all events removal
of a kidney, or even a portion, has been found
to affect the general nutrition of the body.
In some similar way the generative organs,
ovary and testis, especially during their
development, may influence the nutrition of
other parts. This is seen to a marked degree

HIDDEN PROCESSES 155

in many animals, more especially in birds in
the growth of epidermic appendages, such as
the wattles of the male turkey, or the horns of
the stag. In man also, when puberty is reached ,
there are changes in the general nutrition of
the female and in the appearance of the beard
in the male. Such phenomena have been
termed those of complemental nutrition, a
term of little meaning unless we associate with
it the conception that the nutrition of such
organs in some way affects the quality of the
blood, possibly by an internal secretion, and
that this altered quality affects the nutrition
of other organs.

86 We have now to approach what is
known regarding the processes in the living
cell on which the ultimate phenomena of
nutrition depend. Each cell, as we have seen,
is bathed by lymph which has been furnished
by the blood. Under no circumstances does
the blood come into direct contact with the
living tissues outside the vessels. No doubt
the walls of the vessels themselves contain
living elements, and we may regard the wall
of an ultimate capillary as alive. But, so far

156 PRINCIPLES OF PHYSIOLOGY

as the outer tissues are concerned, there is
always the internal medium, the lymph.
This supplies the living cell with matters
prepared, as we have seen, by complicated
processes, and now fit for assimilation. The
lymph also supplies the living matter with
oxygen. How they are actually assimilated
we do not know ; we are now in the most hidden
region of life. In the cell we find living proto-
plasm, and along with it, in many cases,
probably in all cases at some period or other
of the life of the cell, matters that have been
stored up so as to form the elements of
secretions, or the substances necessary for the
vital activities of the cell.

As examples, takes the granules in a secret-
ing cell which has rested for some time, or the
granules in nerve cells, after a period of rest.
If we call the protoplasm a and the stored
matters b, we do not know whether b has at
one time been part of a, or whether a, by some
hidden chemistry, has made b outside of its
own substance. But there is also inter-
cellular matter, which we may call c, and which
has been formed by a. Such inter-cellular

HIDDEN PROCESSES 157

matter we see in the matrix or ground
substance of cartilage, the fibrous material
of osseous tissue, and the substance of
muscular fibre outside the nuclei. The ques-
tion arises — are a, b and c all alive, or are the
phenomena of life to be limited to those
occurring in a, the protoplasm ? There can
be little doubt that life must be limited to the
protoplasm. We can scarcely imagine the
stored matter b or the inter-cellular matter c
to be alive. They do not manifest the general
phenomena of living matter, although they
may be and are highly complex materials.
This brings us then to consider what happens
in a. Undoubtedly there is evidence that
in it there are both anabolic and katabolic
processes, processes both of breaking down
and of repair, as shown by the appearance
in the lymph of chemical substances that
could not have been derived from b but
only from a. According to this view, only
matter taken up into a, assimilated by it,
becomes alive, but it is doubtful if even
here we can draw a dividing line between
what is living and what is dead. We forget

158 PRINCIPLES OF PHYSIOLOGY

that we may here be in a region where there
are no sudden jumps but transitional processes.
Even when matter has been taken up by
the living epithelium of the alimentary
canal, it has been altered. Thus protein
matters, as we have seen, are split up ulti-
mately to form bodies known as amino-acids ;
these, in passing through the living epithelial
cells, are synthetized into serum albumen or
other blood proteins ; these again are probably
modified in the protoplasm of lymphoid tissue
and in lymphatic bodies ; and ultimately the
protein matter, no longer like the same proteim
that it was at first, is now, in the lymph,
brought near the living matter of the cell.
Here we may assume that these prepared
proteins are linked on to the living matter by
hidden chemical affinities, and thus become
incorporated with it. There have been no
sudden leaps, but a series of processes ; there
is no sharp dividing line between what is dead
and what is living. So-called dead matter,
by these processes, has acquired properties
it did not possess before ; and so-called living
matter has by the process that we call nutri-

HIDDEN PROCESSES 159

tion developed new properties which we say
are shown only by matter which is alive.
But only living matter can carry out these
transitions. They cannot be accomplished
by either b or c — only by a.

It is conceivable that it is by purely physical
processes that matters are taken up by the
living cell, so as to reach the protoplasm.
The thin layer of structureless matter lining
the wall of a living cell, and indeed, so far,
constituting the wall, may act like a mem-
brane used in physical experiments on osmo-
tic action. It is well known that such a
membrane may allow certain substances to
pass, while it is impermeable to other sub-
stances. The matters that can pass through
are soluble in the matter forming the mem-
brane, while insoluble substances are rejected.
In the living matter, the protoplasm, we have
seen that chemical processes occur. But
physical chemists know that many chemical
processes are reversible, that is to say, in the
first stage, from certain bodies (a) other
bodies (b) are formed, and in a second stage,
and under different physical conditions, (b)

160 PRINCIPLES OF PHYSIOLOGY

may again become (a) by the chemical
process being reversed. Such phenomena
may happen in a cell, and they may
account for so-called anabolic and katabolie
changes.

CHAPTER XI

THE LIBERATION OF ENERGY

87. WE have already seen that energy is
liberated by the splitting up of complex
into simpler substances. By liberation we
mean the setting free of energy as kinetic
energy. Thus by the explosion of gunpowder
or of gun cotton, the mass is resolved into
gases at a high temperature, and the expansion
of these gases is used to drive a projectile
from a cannon. The energy of the explosive
is resolved into heat and motion. This latent
energy may be set free by communicating to
it the shock of a hair trigger, and the amount
of energy of the hair trigger is infinitesimally
small compared with that set free by the
explosion. The energy of the trigger may be
regarded as a liberator of the energy in the
explosive. This analogy helps in understand-
ing the phenomena in certain tissues. Thus

L 161

162 PRINCIPLES OF PHYSIOLOGY

in muscular tissue, energy is latent when the
muscle is at rest, but when the nervous impulse
reaches it by travelling in a nerve the muscle
contracts, becomes warmer and does work by
motion, in one form or another. The nervous
impulse is the liberator, — the muscle substance,
along with the chemical phenomena we have
considered, liberates energy as heat and motion.
In like manner, energy is stored up in all
living matter, in the secreting cell, in the tissues
of the nervous system, and probably in other
living tissues, and it is set free by a nervous
impulse. This explains why heat is developed
in a secreting gland during its activity, and
if we had adequate experimental appliances,
we should find evidence of heat in all vital
activities.

88. Heat is also produced in the body in
other ways. The friction of the blood on the
walls of the vessels as it is driven along in the
circulation is resolved into heat, in other
words all the energy of the circulation becomes
heat. In like manner the movements of
organs causing friction produce heat. But
the great sources of heat are the phenomena

THE LIBERATION OF ENERGY 163

that occur in muscle and in secreting glands,
The amount of heat produced in other ways is
comparatively small. The body may also
receive heat by the ingestion of hot food or
drink and by conduction and radiation from
the surrounding medium. The amount of
heat thus produced in a living body is very
large, and if it were not lost from the body in
in some way, the mean temperature of the
body would soon rise to a degree incompatible
with life. But the arrangements for the
removal of heat are efficient. It is thrown
off from the body into the surrounding
medium by conduction and radiation if the
temperature of the medium is below that of the
mean temperature of the body. Heat is lost
by, in some circumstances, taking cold food
or drink, or by the evacuations. It is also
lost by becoming latent in the evaporation of
sweat from the surface of the skin, that is to
say heat is lost in converting the sweat into
vapour. Thus the body is maintained in
normal circumstances at a mean temperature
in the armpit of 98.40° Fahrenheit.

89. If we estimated all the heat entering the

164 PRINCIPLES OF PHYSIOLOGY

body and added it to that produced in the
body itself, say in twenty-four hours, it would
normally be about equal to that given off by
the body in the same time. The income and
the expenditure would be about equal, and
the mean bodily temperature would be fairly
constant. If more heat were produced than
could be* got rid of, as in fever, the mean
temperature would rise, whereas if less heat
was produced than was given off the mean
temperature would fall. It would appear that
vital activities can be carried on efficiently
only within a narrow range of temperature.
Hence the danger to life, in many diseases, if
the temperature rises above 104° or 105°. A fall
of temperature ten or twelve degrees below
normal temperature is not so dangerous. The
activity of the skin in producing sweat, and
the evaporation of the sweat, is the great
regulator. Hence there is danger to life in
certain parts of the tropics where there may be
an air temperature above 98° F., and where the
air, at that temperature, may be saturated
with aqueous vapour. Here evaporation from
the skin is impossible, heat penetrates from

THE LIBERATION OF ENERGY 165

without, and the mean temperature of the
body must gradually rise.

90. Energy is also liberated as motion by the
contractions of the muscles. The muscles may
either perform internal work, — as the beating
of the heart, the movements of respiration, the
movements of the limbs on the trunk, the
movements of the involuntary muscles, as of
the bladder and bowel, — or external work, as
in locomotion or in mechanical labour. All
internal movement is ultimately resolved
into heat. The external work can also be
measured and expressed as heat, and thus the
total energy of the body in twenty-four hours
liberated by a man doing say eight or ten hours
of hard work can be calculated. Further,
the energy represented by the complete com-
bustion of a diet sufficient for a man doing
this work and producing heat during twenty-
four hours can also be calculated. It can be
shown that there is a balance struck between
income and expenditure, and this balance,
in ordinary circumstances, is fairly constant.
It becomes interesting to consider man as a
transformer of energy with special reference

168 PRINCIPLES OF PHYSIOLOGY

to the amount of energy he can liberate as
mechanical work and the ratio of this amount
to the amount of energy appearing as heat.
The best results show that about 25 per cent,
of the available energy appears as work, with
75 as heat. This compares favourably with
many human contrivances. The best steam-
engine can only give about 12 J per cent, of
the energy produced by complete combustion
of the fuel, but gas or petrol engines can do
much better — as much as 96-98 per cent, of
energy can be transmuted by certain electrical
contrivances. The heat of the engine, how-
ever, is a real loss of energy, and all engineers
strive to reduce it to a minimum, but the heat
of the body is one of the all-important conditions
of its mechanism. The source of error in all
such estimations is that food stuffs are never
completely oxidised in the body, and further
that the methods followed by the engineer in
measuring the output of energy are different
from those of the physiologist. Still the
general statement is fairly correct.

91. In some animals energy is liberated in the
form of electrical energy or light, as in the electric

THE LIBERATION OF ENERGY 167

fish and the glow-worm and fireflies. Even
in the human body there are also electrical
phenomena. Every contraction of a muscle,
the secretion of a gland, and probably also
nutritional changes in the tissues, are asso-
ciated with electrical phenomena, which may
be demonstrated by a sensitive galvanometer
and suitable methods. It can be shown that
antecedent to every muscular contraction
there is generated a change in the electrical
condition of the muscle. Whether this elec-
trical state is an expression of the chemical
changes in the muscle, on which motion and
heat depend, or whether it is an isolated physi-
cal phenomenon, it is difficult to say. Even
the heart beats are associated with electrical
phenomena. Living nerves also show elec-
trical changes similar in kind to those found
in muscle. It is significant that the electrical
organs of fishes are modifications of muscles
or glands. Thus the electrical organs of the
Torpedo occellata (of the Mediterranean), of
the Gymnotus electricus or electric eel (of the
Orinoco), and of the skates (Raid) are all
modifications of muscle, while that of the

168 PRINCIPLES OF PHYSIOLOGY

mud-fish of the Nile, Malopterurus electricus,
is a modification of glands of the skin.

92. Further, it would appear that modern
views as to the nature of solutions, in relation
to electrical and other actions, must also be
applied to the living tissues. Thus salts may
act not as salts, but in solution the elements
may exist separately as ions, related to either
the positive or negative poles of a current,
or carrying electrical charges, and that
physiological activities may vary according
as the anion (positive pole ion) or the kation
(negative pole ion) comes into play. There are
thus in living matter subtile phenomena of
which we yet know very little.

CHAPTER XII

THE REGULATING MECHANISM. NERVOUS
SYSTEM

93. THE nervous system controls and regulates
all the organs and even the tissues of the body
while, at the same time, all the organs contri-
bute to its upkeep and nutrition. In a sense,
too, it binds together the various organs and
systems of organs so that they act harmoni-
ously and it confers individuality on the body
It is the channel, also, by which influences from
the external world act on the central nervous
organs through the organs of sense. Finally
it is the seat of consciousness and of all mental
operations. The nervous system is highly
specialized. At the beginning of development
it arises from the ectoderm of the embryo
and it pursues its own mode of development
So necessary is it to the well-being of the body

that it is nourished and has its waste products
169

170 PRINCIPLES OF PHYSIOLOGY

removed by special arrangements, while it is,
as far as possible, protected from injury.

94. Essentially, the nervous mechanism
consists of centres, nerves, and nerve-end
organs. The centres are in great masses
constituting the brain and spinal cord, and
in smaller masses found scattered here and
there, known as ganglia. The nerves are
found almost everywhere, as whitish cords,
varying in calibre from the largest nerves,
such as the sciatic in the back of the thigh,
down to minute filaments invisible to the naked
eye and requiring the use of the microscope
for their detection. Each nerve is composed
of minute fibres, all of microscopic dimensions,
and each showing a central rod or axis,
surrounded by a sheath, called the white
substance, and this, in turn, usually covered
by a thin membrane, the neurilemma. These
matters are all of soft consistence and are
apparently structureless, but, by special
methods, details of structure may be seen.
Thus the central axis is sometimes composed
of fine fibrils, and the surrounding matter,
the white substance, is composed of elongated

THE REGULATING MECHANISM 171

flattened nucleated cells. The analogy of
a nerve-fibre to a copper wire surrounded
by an insulating sheath is striking, the wire for
conduction representing the central rod or
axis, while the insulating sheath is the white
substance. Still it is only an analogy. Nerve
fibres vary much in diameter. Many have no
white substance ; primitive fibres are desti-
tute of it, and it makes its appearance late
in development. Nerves consisting of bundles
of fibres divide and subdivide into more
and more delicate fibres, until, as already
pointed out, they are so minute as to be
invisible to the naked eye. If we trace the
axis of a fibre to its beginning we find that it
always originates from or in a nerve cell.

95. Suppose a nerve were laid bare and it
were stimulated, say by gentle shocks of
electricity, so feeble as barely to be felt by the
tip of the tongue, one or more results might
follow : (1) a muscle might contract, and then
we call the nerve motor because it produces
motion of a muscle ; (2) a gland might begin
to secrete, showing the action of a secretory
nerve ; (3) blood vessels might diminish in

172 PRINCIPLES OF PHYSIOLOGY

calibre as occurs when a vaso-motor nerve is
acted on ; (4) pain might be felt when the
nerve is sensory and carries impulses to the
brain ; (5) if it were a nerve of special
sense, such as the optic or the auditory
nerve, there would be a sensation of light or
colour, or sound ; (6) in an electric fish, the
result might be an electric shock from the
electric organ These phenomena are often
complicated. Sometimes we have a nerve
that has only one function, that of causing,
say, motion or secretion, but usually a large
nerve consists of fibres having different
functions. For example, a nerve may contain
both motor and sensory fibres, and might serve
in part to excite movement, and in part to
convey impressions of touch or temperature or
pain. When a fibre is stimulated no physical
change can be seen with even the highest
powers of the microscope. Nerves may also
be conveniently classified for physiological
purposes into (a) centrifugal, those conveying
impulses from nerve centres outwards, and
centripetal, or those carrying impulses from
the outer parts of the body to nerve centres.

THE REGULATING MECHANISM 173

96. A change passes along a fibre when stimu-
lated. This may be termed a nervous impulse.
We do not know what this change is ; no
movement of matter can be observed ;
obscure chemical phenomena have been noted,
as shown by the necessity for oxygen and the
production of carbonic acid. Electrical
charges can be detected which seem, like the
nervous impulse, to pass along a nerve, but
are not to be confounded with it ; and the
impulse travels along the fibre with a velocity
of only 200 feet per second, incomparably
slow, as compared with the velocities of
electricity or sound. Recent observations,
made with a new form of galvanometer —
Einthoven's string galvanometer — a very sen-
sitive instrument, seem to show that the
velocity is considerably greater than has
been supposed. It would seem also that when
the fibre is stimulated at any point the
impulse travels in both directions. Nerve-
fibres are conductors, but, unlike an electrical
conducting arrangement, they are not only
conductors, because, at the point stimulated,
a change is there generated which is then

174 PRINCIPLES OF PHYSIOLOGY

transmitted, and apparently with accumulat-
ing energy. So far as can be observed, all
fibres act alike.

97. Nerves, composed of fibres, may be
divided, and if rejoined they will re-unite
and act as before. This has led to the experi-
ment of dividing two adjacent nerves, (a)
motor, and (b) sensory, and reuniting the
ends so that the upper end of a is joined to
the lower end of b, and vice versa ; they may
then unite and functions may be restored.
It is evident that if the upper end of a was
motor and conducted downwards, while the
lower end of b was sensory and conducted
upwards, the nervous impulse in one or the
other nerve must now conduct in the reverse
direction to what it did before division
But if a nerve is only a sensitive conductor, why
are the results of stimulation so various ?
It is due to the fact that the result depends
on the apparatus at the end of the nerve. If
the fibres end in muscle, there will be motion ;
if in a gland, secretion ; if in a blood vessel,
change of calibre ; if in a special part of the
brain, sensation or pain. The analogy to

THE REGULATING MECHANISM 175

electrical arrangements is helpful, but we
must be careful to remember it is only an
analogy. Confusion results from introducing
words that have a definite meaning to electri-
cians, such as resistance. There is no evidence
of any such phenomenon in nerve. If,
however, we take the analogy of an electrical
current, it might be caused to produce light,
heat, motion, or the decomposition of water.
All would depend on the arrangements at the
end of the wire conducting the current.
Finally, as a nerve is a sensitive conductor,
irritation at any part of its course will always
produce the same effect. We may irritate a
nerve close to a muscle or far from it, but
the result will be a muscular contraction.
We may irritate a nerve near the sentient
brain, or far from it, but the resultant sen-
sation will be the same, only, in this case,
the origin of the impulse will be referred by the
mind to the beginnings of the sensory nerve,
say in the skin of the hand. An illustration
will assist the reader. Suppose a telegraph
message were transmitted from Glasgow to
Edinburgh, and that the clerk in the office in

176 PRINCIPLES OF PHYSIOLOGY

Edinburgh was in the daily habit of receiving
such a message ; it would not matter to him
if one day the message was transmitted to
him from a station half way between Edin-
burgh and Glasgow ; he would still believe it
came from Glasgow and he would, if necessary,
reply to that city.

98. It is convenient, in the next place, to
consider the end-organs. These are highly
specialized organs found at the ends of
centrifugal nerves, and at the beginnings of
centripetal nerves. The endings of motor
fibres in muscular tissue are an example of the
first, and the structures in the skin connected
with the sense of touch represent the second.
End-organs are adapted to the stimulation
of certain tissues by the nervous impulse
coming from a centre or to the awakening
of a nervous impulse by stimuli acting on
the end-organ. Thus we have end-organs
in muscle at the termination of motor
fibres ; nerve fibres can be traced into
actual contact with secretory cells and blood
vessels ; and, in electrical organs, into special-
ized structures constituting the electric tissue

THE REGULATING MECHANISM 177

On the other hand, each organ of a special
sense has a terminal organ, such as the retina
in the eye, the various organs in the skin
connected with touch, and the wonderful
arrangements in the internal ear suitable
for being acted on by the vibrations of sound.
There are also end-organs in muscle and in
tendons by which nervous impulses are
awakened in these structures by movements,
and the impulses so generated are carried
to nerve centres. We do not know how end-
organs act. Those of muscle, for example,
may in some way excite the muscle protoplasm
so as to cause a kind of physiological explosion
ending in the inevitable contraction. We do
not know how the nervous impulse acts on
a secreting cell. Sensory end-organs, on the
other hand, as we shall see in considering
the senses, are each adapted to the re-
ception of their specific kind of stimulus.
Thus the retina is adapted to light, the
structures in the internal ear to sound, the
structures in muscle and tendon to pressure,
and so on

99. We have next to turn our attention to

H

178 PRINCIPLES OF PHYSIOLOGY

the central organs, which are by far the most
complicated and most difficult to understand.
They consist of the brain, the spinal cord or
marrow, and ganglia. Ganglia are small
masses of nerve matter found in many parts
of the body, and they abound in many organs,
as in the heart and in the mesentery. Such
small nodules of nervous matter consist of
supporting tissue, nerve cells, and nerve fibres.
From one point of view, the spinal marrow and
the brain may be regarded as masses of ganglia
fused together during countless ages of evolu-
tion. All ganglia, be they simple or complex,
are known to be composed of certain morpho-
logical elements or structural units. These
units are supported and protected by a
specialized form of tissue, the neuroglia,
which, however, is not ordinary connective
tissue, although that may also enter into the
composition of nervous structures. The units
are known as nerve-cells, or neurones. These
vary much in general form and size, but
they have certain general characteristics.
They are composed of protoplasm in which
there is a well-defined nucleus, and both in

THE REGULATING MECHANISM 179

the cytoplasm (protoplasm of the cell) and
in the nucleus, there are fine fibres and
networks, while chromatin is abundant in
the nucleus. In the protoplasm of the nerve
cell we find numerous granules. These are
more abundant after the cell has rested for a
while, and they seem to be used up during the
period when the cell is active. The exhausted
cell, during the next period of rest, again
becomes crowded with granules as it revives.
Thus it behaves like a secreting cell. Pro-
cesses, or as they have been called, poles, issue
from the cell. These are sometimes few in
number, but in many cases each cell may
have four, five, or six processes. All of these
processes, except one, divide and subdivide
so as to form smaller and smaller processes,
like a branch of a tree dividing until we
reach the ultimate twigs. The branch of
a tree seen against a winter sky is a picture
of the arrangement. The remaining process
is the beginning of the axis of a nerve fibre,
around which the white substance is developed
at a later period. The ultimate unit of the
nervous system therefore is now designated

180 PRINCIPLES OF PHYSIOLOGY

as a neurone, the fine processes produced by
some of the poles constitute branchlets or
dendrites ; a mass of dendrites forms a dendron,
or tree-like structure, and the process that is
the origin of a nerve-fibre is the axon, or
central rod. Next, imagine the branches
of two adjacent trees freely intermingling, but
not touching each other. This is a picture
of the relation of two or more neurones.
The dendrites do not form a network, as was
once supposed ; they do not even touch ;
there is, as has been aptly said, contiguity
but not continuity of structure Where den-
drites come close together without touching,
as if they were almost clasping, we have
what is called a synapsis. The dendrites
may sometimes form a network in close
proximity to, or even enveloping, the body of,
an adjacent neurone. This network is called
an arborization. We do not know what
phenomena occur at a synapse or arbori-
zation. The axon is a process of a neurone,
and it may be of great length or it
may be short. Thus axons from neurones
in the lower part of the spinal cord, for

THE REGULATING MECHANISM 181

example, may extend unbroken to the foot.
It would appear they may divide and sub-
divide, and as the mass of matter must increase
as the fibre passes onwards, the material
forming the conducting central part of a
nerve-fibre must also increase. This has-
been well established in the electric fish
Malopterurus, In this animal the electric
organ in each half of the body is set into action
by the activity of one gigantic neurone in
each half of the spinal cord, each minute
portion of the electric organ is supplied by
a nerve fibre, and the sum of the diameters
of these fibres is many thousand times greater
than the diameter of the axon where it issues
from the giant neurone,

100. The central nervous system is built up
largely of masses of neurones, supported by
neuroglia. These masses constitute what is
called the grey matter, found in the centre of
the spinal marrow and in and more especially
on the surface of the brain. Grey matter
is always supplied by a very rich plexus of
capillaries formed by the subdivision of arteri-
oles ramifying and subdividing in the mem-

182 PRINCIPLES OF PHYSIOLOGY

branes covering the brain and cord. A great
blood supply always means intense physio-
logical activity. Along with the grey matter,
in the central nervous organs, brain and cord,
there are strands of nerve fibres constituting
the white matter. This is not so richly supplied
with blood. In both brain and cord there are
.special arrangements for removing waste
products. In a sense the organs lie in lym-
phatic sacs or bags, and while there are no
special lymphatics, each minute vessel is
surrounded by a sheath, perivascular so-called,
which contains lymph. The grey matter is
thus richly nourished, while waste products
are quickly got rid of and carried off.

101. Little is known of the activities of a
nerve-cell. As already pointed out, granules of
matter are used up, but we do not know what
is the composition of these granules (Nissl's
granules). Chemical substances of a protein
nature, and especially rich in phosphorus com-
pounds, abound in the protoplasm of a nerve
cell. The activity of the protoplasm depends
more on an ample supply of oxygen and the
removal of waste matters than any other kind

THE REGULATING MECHANISM 183

of protoplasm. It is doubtful if the protoplasm
of a neurone, say in the brain, can act for longer
than a few seconds without oxygen, and the
removal of waste matters. Hence there is
immediate loss of consciousness if the supply
of blood is cut off from the cerebrum, and if
the quality of the blood be altered by the
presence of even small amounts of poisons
the effect is quickly felt. Nervous matter is
also extremely sensitive to shocks or variations
of pressure. Thus a sudden concussion will
often produce unconsciousness. The activities
of the nervous system, and especially mental
activities, depend on the interplay between
grey matter and blood, and the limit of
adaptation as regards blood supply, quality
of blood, and temperature, is apparently
very small. Nearly all the other functions of
the body, in a sense, are working towards
the end of the adequate nutrition of the grey
matter.

102. There are certain definite mechanisms
connected with nervous activity that must
now be noticed. Sometimes if a sensory nerve
is stimulated, there may be no sensation or

184 PRINCIPLES OF PHYSIOLOGY

pain, but movement of a muscle or a group of
muscles, possibly in some distant part of the
body. This is known as a reflex action. It
implies a sensory nerve, by which an impulse
is carried to a centre, a centre in which a
change occurs, the nature of which we do not
know, and a motor nerve carrying an impulse
to muscles and causing a contraction. The
term reflex, although in general use, is mislead-
ing, as it suggests something reflected like a
ray of light by a mirror ; but we have no
better word at present. We know that
something occurs in the centre, as time is
occupied. Assuming the velocity of the
nervous impulse and a given length, both of
(a) sensory and of (b) motor nerve, more time
is occupied in a reflex action than the sum of
times occupied in a and b. This increased
time is in c, the centre. Reflex mechanisms
play an important part in the body Many
are very complicated, involving several sensory
and several motor nerves, and even the
centres may be complicated. As an example
of a simplex reflex, we may take the move-
ment of winking of the eyelids. Here the

THE REGULATING MECHANISM 185

sensory nerve may either be the sensory nerve
of the skin and of the eyeball (the fifth cranial
nerve), or the optic nerve itself through the
retina, while the motor nerve is a branch of
the seventh cranial nerve, the facial, supplying
the muscle that closes the eyelids (the orbicu-
laris palpebrarum). The movements of swal-
lowing and the respiratory movements are
examples of highly complex reflex actions,
involving many nerves and many muscles.
We may or may not be conscious of reflex
movements, but they cannot be arrested by
an effort of the will. Many movements, at
first consciously performed, become reflex
without consciousness, as in locomotion, play-
ing on an instrument and working a machine.
The centres are found in the brain and cord.
103. The nervous mechanisms we have con-
sidered cause increased activity. It is prob-
able that even while apparently at rest
molecular phenomena are occurring in nerve
cells. Thus certain nerve fibres issuing from
neurones in the spinal cord pass to the muscles-
of the limbs and keep these in a state of partial
contraction or tonics, as it is termed. In this

186 PRINCIPLES OF PHYSIOLOGY

way muscles are not loose but firm and slightly
contracted, even while at rest. And when a
more powerful nervous impulse reaches them,
they are ready to contract efficiently. To use
a nautical phrase, the muscles are not on the
" slack " but always " taut," and no energy
is lost in " gathering them in." But certain
nerve fibres have the power, not of causing,
but of restraining activity. Such nervous
actions are said to be inhibitory. A striking
mechanism of this kind is seen in connection
with the innervation of the heart

104. This organ has numerous little ganglia
in its own substance, and possibly these may
have to do with its rhythmic contractions,
although this is doubtful. Two great pairs of
nerves give off branches that can be traced into
the heart. These are the vagi, which come from
the medulla oblongata, the portion of the spinal
cord inside the skull, and the sympathetics,
that arise from a chain of ganglia running along
each side of the vertebral column. The fibres in
these ganglia are derived from the cord by the
anterior roots of the spinal nerves. Suppose the
heart to be beating rhythmically, stimulation

THE REGULATING MECHANISM 187

of the sympathetic in the neck causes it to beat
slightly faster, but stimulation of the vagus,
also in the neck, causes the heart to beat more
slowly ; stronger stimulation may stop the heart
altogether, and it will then be found that it is
arrested with all its cavities dilated, that is
to say, the muscle substance is at rest. This
action of the vagus is said to be inhibitory or
restraining, while that of the sympathetic is
accelerating.

105. Such inhibitory phenomena have been
found in connection with many nerve centres.
For example the sympathetic is the nerve
that acts on the muscular walls of small
vessels, keeping them in a state of partial
contraction, and thus, as already explained,
maintaining a high blood pressure. If this
pressure rose too high, the heart would have
more work to do in driving the blood onward
with increased resistance. The centre (vaso-
motor), which thus acts through the sympa-
thetic, is in the medulla, and it is assumed that
impulses are constantly passing from it to the
vessels. This centre, however, may be inhib-
ited by the action of a nerve passing from

188 PRINCIPLES OF PHYSIOLOGY

the heart upwards. If we stimulate this
nerve, called the depressor, impulses pass
upwards which inhibit the centre in the
medulla, throwing it, as it were, out of action,
with the result that the arterioles dilate and
the blood pressure falls. Other nerves appar-
ently may affect this centre in an opposite
way, causing it to act more powerfully, and
therefore raising the blood pressure. These
are called pressor-nexves, in opposition to
the depressors. Most sensory nerves act as
pressor-nerves. Nerve centres are thus often
under the action of impulses having contrary
effects, while they are also influenced by the
quality of the blood circulating through
them. Inhibitory mechanisms play an import-
ant part in the nervous machine. Probably
the restraining powers of what we term the
will have a physiological basis of this nature.
106. The spinal cord may be regarded as a
series of segments combined together to form
one mass. Each segment has a pair of spinal
nerves, each connected with the central grey
matter by two roots. The anterior root
consists of motor fibres carrying nervous

THE REGULATING MECHANISM 189

impulses outwards from neurones in the
grey matter. These fibres mostly supply the
muscles of the trunk and limbs on the same
side. They also pass to blood vessels, and
probably to glands, through the ganglia of
the sympathetic The posterior roots con-
sist of fibres that convey sensory impulses
into the cord. On this root there is a gan-
glion containing neurones. Sensory fibres,
coming from the skin, muscles, and other
organs, are related to the neurones in the
ganglia, and from these neurones new fibres
spring, which carry impulses into the cord.
The neurones in the ganglia on the posterior
roots are the first receiving stations of
sensory impulses. Many of such impulses are
then conveyed upwards to the brain, and may
give rise to sensations of various kinds. Each
segment of the cord, however, is connected with
a number of segments both above and below it.
Many of the sensory fibres of the posterior roots
come into relation writh neurones in the cord
in one or more segments. From these neur-
ones axons arise, which find their way into
the anterior roots and thence to the muscles.

190 PRINCIPLES OF PHYSIOLOGY

Thus we have many reflex mechanisms,
which do not involve higher centres. Sensory
fibres pass up the back part of the cord to
higher and higher centres, calling forth higher
reflex mechanisms, but many, as already
indicated, ultimately reach the sensory part
of the cerebrum, and give rise to consciousness or
sensations of various kinds. The sensory paths
are therefore mainly in the posterior part of
the cord, and these pass ultimately to the brain
on the opposite side, the crossing taking place in
the cord and in the medulla. Thus sensory im-
pulses from the right side ultimately reach the
left cerebral hemisphere, and vice versa. Many
sensory impulses also reach the cerebellum, or
lower brain. Voluntary motor impulses arise
in the cerebrum, pass downwards through the
lower parts of the brain, cross to the other side
in the bulb or medulla, run down the anterior
part of the cord, and, as they pass down, they
turn into the grey matter and end by arboriza-
tions (like the twigs of a tree) that are close to,
but do not touch, the dendrites of large
neurones in the grey matter. These give off
the axons that become the nerves of the

THE REGULATING MECHANISM 191

muscles Thus these large neurones in the
anterior part of the grey matter of the cord
have fibres reaching them from the posterior
roots, and are thus the mechanism of reflex
acts, but they are also related to the upper
cerebral centres so as to be the mechanism
for voluntary acts. It is important to notice
that the axons of neurones in the higher
parts of the nervous system may become
related by arborizations to neurones lower
down, and the reverse is also true, lower
neurones becoming similarly related to higher
ones. It may only be an analogy, but the
whole mechanism suggests a series of relays
such as one might conceive in a very extensive
telegraphic system. In a telegraphic relay
the current may be caused to work a mechan-
ism a long way off ; by this mechanism another
current may be started, and so on, until the
terminal station is reached.

107. It would appear that in movements,
such as those of locomotion, caused by
antagonist groups of muscles, such as those
that bend the forearm on the arm (flexors)
and those that extend the arm (extensors),

192 PRINCIPLES OF PHYSIOLOGY

we have a kind of double nervous mechanism.
Thus, when a nervous impulse causes flexors
to contract there is, at the same time, an
influence which inhibits or restrains the
extensors. The nervous machinery therefore
is often very complicated.

108. The part of the cerebro-spinal system
within the skull consists of the following struc-
tures : — (1) a double chain of large masses
of grey and white nervous matter, forming
from before backwards ; (a) the corpora
striata, (b) the optic thalami, and (c) the
corpora quadrigemina ; (2) still farther back
(a) the pons, (b) the bulb or medulla ; (3)
covering the whole of these masses we find the
two hemispheres of the cerebrum ; and (4) on
the back of the pons and bulb and below the
posterior part of the cerebrum, we find the
cerebellum. These structures are all connected
with each other by strands of white matter
formed of nerve fibres, while grey matter is
found in masses or nuclei. The fibres
carry impulses either upwards or down-
wards. There are also numerous fibres
passing from one lateral half of the brain to

THE REGULATING MECHANISM 193

the other side. The grey matter in the pons
and bulb gives origin to fibres which run
into the great cranial nerves, analogous
to, but much modified from, the pairs of
spinal nerves. We may shortly indicate
the functions of such nerves. Some of the
cranial nerves are entirely motor, convey-
ing impulses to the muscles of the face on
the opposite side, such as the seventh nerve,
that innervates the muscles of expression ;
others are entirely sensory, such as the optic
and the auditory ; while a third class are
sensori-motor, containing both sensory and
motor fibres, such as the fifth, the sensory
nerve of the face, but which also contains
motor fibres for the muscles of the tongue.

109. The bulb or medulla contains centres
connected with respiration, the action of
the heart, and the blood vessels. The latter
is the vaso-motor centre already referred
to. In the bulb also originate the roots of
some of the cranial nerves. Passing through
it we also find the motor and sensory
paths connecting the brain with the spinal
system of nerves. It is important to notice

194 PRINCIPLES OF PHYSIOLOGY

that both sensory and motor, especially
motor, tracts cross in the bulb. This part
of the brain is therefore all important to life.
If it is destroyed the respiratory, cardiac,
and vascular mechanisms quickly cease. It is
also the seat of reflexes of a complicated
character, such as those of swallowing.

110. The bulb may also be regarded as
the most posterior part of the brain, or
as the portion of the cord within the
skull. It is in a sense one of the most
important centres of the body because,
as already mentioned, it contains centres
for mechanisms absolutely essential to life.
A study of its functions also illustrates
several fundamental principles. Although not
of large dimensions it contains, in addition to
fibres passing through it, and conveying
impulses upwards and downwards, the follow-
ing centres : (a) respiratory centres ; (b)
cardiac or heart centres ; (c) vaso-motor
centres for the peripheral blood vessels ;
and (d) centres for swallowing. As each
centre is double, owing to the bilateral sym-
metry of the nervous system, there are at

THE REGULATING MECHANISM 195

least eight nuclei of grey matter in the
medulla, all of which are important. The
neurones in this grey matter are all intimately
related to each other. The bulb is also
richly supplied with capillary blood vessels,
and it lies practically in a lymphatic space
while perivascular lymphatic channels sur-
round its vessels. Waste matters are thus
quickly removed. All the blood vessels in
the bulb are of remarkably small diameter,
as one would expect. To and from this
centre, or rather group of centres, there run
numerous nerve fibres connected with the
vagi or pneumogastric nerves, and some of
the cranial nerves. Fibres also pass into the
sympathetic chain of ganglia.

111. As already mentioned, the bulb has
to do with the innervation of the heart and of
the respiratory mechanism. Both of these
movements are rhythmic in their character.
We feel this in the beat of the heart and in
the regular periodic movements of inspiration
and of expiration. If these movements depend
on the bulb, the question arises as to whether
or not the bulb acts automatically. Is there

196 PRINCIPLES OF PHYSIOLOGY

such a thing as automatic action in the nervous
system ? One can imagine a nerve centre
acting automatically. Suppose that in some
way nervous energy is stored up in the centre
until there is such a state of tension as to
cause a discharge along certain nervous
paths. This discharge would lower the tension
and there would be an interval during which
energy would be again stored until the next
discharge, and so on. This would be an
automatic mechanism. Research has shown,
however, that this is not the way in which the
nervous centre works. It is not automatic,
but it is influenced, first, by the quality of the
blood flowing through it, and it is, in the
second place, controlled or regulated by
nervous impulses coming by sensory paths
from the periphery. Consider this with refer-
ence to the respiratory mechanism. In-
spiration mainly introduces fresh oxygen
into the blood, and both during inspiration
and expiration there is the removal of carbonic
acid. When the blood contains a certain
proportion of oxygen, even although carbonic
acid is also present, it is bright red arterial

THE REGULATING MECHANISM 197

blood ; but when it contains more carbonic
acid and relatively less oxygen, it is dark
purplish-hued venous blood. Again, if we
breathe deeply a number of times in succession
so as to introduce as much oxygen as possible,
we can then " hold the breath," that is to say,
we can for a time cease breathing. Divers
do this before they make their plunge into the
sea. In physiological language, blood con-
taining an excess of oxygen produces a state
called apnoea, during which respiration is sus-
pended. On the other hand, if the blood
contains more than a certain amount of
carbonic acid, so as to be highly venous, there
is a tendency to make rapid movements
of inspiration so as to get rid of the excess
of carbonic acid and introduce more oxygen.
This happens in asphyxia, produced from any
cause. These phenomena can be accounted
for if we consider the influence of the kind of
blood circulating through the respiratory
centre. When the blood is rich in oxygen, the
centre is not stimulated, but when deficient in
oxygen and rich in carbonic acid, the centre is
stimulated so as to produce inspiratory

198 PRINCIPLES OF PHYSIOLOGY

movements. Two respiratory centres have
been by some assumed to exist in the bulb —
an inspiratory and an expiratory centre.
Then carbonic acid may be supposed to
stimulate the inspiratory, while oxygen might
either stimulate the expiratory or produce no
effect. There can be no doubt, however we
may theoretically explain the facts, that the
quality of the blood affects the respiratory
centres.

112. But the centres for respiration are also
influenced by nervous impulses coming from
the periphery. The lungs are supplied by
the vagi or pneumogastric nerves. These
contain both sensory fibres for carrying
nervous impulses upwards to the bulb, where
the vagi originate, and motor fibres which
supply the muscles of the larynx and the
muscular fibres in the walls of the bronchial
tubes. The larynx is highly sensitive through
the medium of a sensory nerve, the superior
laryngeal branch of the vagus, which leaves
the main trunk in the neck and is dis-
tributed to the lining membrane of the
larynx. Experiment has shown that if the

THE REGULATING MECHANISM 199

vagus be divided in the neck then irritation
of the upper end of the nerve causes deep
inspirations, and that strong stimulation
may stop breathing with a kind of spasm at
the end of an inspiration. This shows that the
impulses coming from the lungs are carried
upwards to the respiratory centre in the bulb,
and that they more especially stimulate
inspiration, possibly by acting on the in-
spiratory centre. On the other hand, stimu-
lation of the superior laryngeal branch of the
vagus causes expirations, and strong stimu-
lation may stop respiration at the close of an
expiratory spasm. Impulses therefore coming
sometimes from the larynx excite expirations.
Now one can imagine the terminal fibres of
the vagus in the lungs to be stimulated by
venous blood ; impulses would then be sent
to the inspiratory centre in the bulb. This
would be stimulated, with an inspiration as
the result. But inspiration is a muscular act
involving the diaphragm and the muscles that
raise the ribs, while expiration is an act mainly
due to an elastic recoil of the lungs and of the
walls of the chest. Consequently there is no

200 PRINCIPLES OF PHYSIOLOGY

necessity for calling into play the expiratory
centre except occasionally when there is
more or less obstruction to the free exit of
air from the lungs. This explains the
mechanism of coughing, which consists of
violent expiratory efforts. But the inspira-
tory centres may be influenced through other
nervous channels. Strong stimulation of
almost any sensory nerves will cause inspira-
tions. Slapping the skin with a wet cloth,
plunging into cold water, a sudden draught of
cold air, pain, will usually cause inspirations.
Probably the first breath of a newly-born
child is thus excited. Finally, impulses may
come to the respiratory centres from the
higher centres in the brain. Thus, within
narrow limits, we can voluntarily control the
breath. When by certain morbid changes in
the higher centres, there is unconsciousness,
breathing may still go on, but in a curious,
fitful way, as if a mechanism regulating the
respiratory centres had been interfered with.
So that the respiratory centres are maintained
in a condition of physiological equilibrium by
numerous nervous impulses coming to them by

THE REGULATING MECHANISM 201

sensory filaments, and also by the quality of
the blood flowing through them. They are
not automatic.

113. The same is true of the other centres
in the bulb. Thus the cardiac centres, acting
downwards through the vagi, tend to inhibit or
restrain the contractions of the heart, as already
explained, while fibres that find their way from
the cord into the sympathetic have an accele-
rating action (p. 187). We may therefore
assume the existence in the bulb of inhibitory
and accelerating cardiac centres. These again
are influenced by peripheral impulses. From
the heart impulses may pass to the bulb centres
and then to the cerebral centres and from them
again downwards to the centres in the bulb.
Impulses may also reach the cardiac centres
along any sensory nerve, and in this way there
may be a degree of inhibition or acceleration,
or impulses may come from the seat of con-
scious emotion in the cerebral centres and
terror may cause the heart momentarily to
miss its beats.

114. In a similar way the vaso-motor centres
in the bulb may be influenced. The action of

202 PRINCIPLES OF PHYSIOLOGY

this centre is to maintain the arterioles in a
certain state of contraction, and this, as already
explained, keeps up the blood pressure. But
this centre may be inhibited by impulses
coming from the heart by the depressor
nerve (p. 188), while the centre may be stimu-
lated to greater activity by many sensory
nerves which thus act as pressor nerves and
raise the blood pressure. Again, the centre
may be influenced by impressions coming to
it from the brain centres, thus producing the
blush of shame or the pallor of fear. It has
been found that the vaso-motor centre pos-
sesses a kind of inherent rhythm. Thus when
all peripheral impulses have been prevented as
far as possible from reaching it, the blood
pressure still goes through a slow series
of variations — that is to say, the muscular
walls of the arterioles have a slow rhythmic
movement, contracting and expanding in
obedience to impulses still coming from the
vaso-motor centre. (Traube-Hering curves of
blood pressure).

115. These nervous mechanisms are pictures
of the mode of action of all nerve centres.

THE REGULATING MECHANISM 203

There is no automatism, at all events in
the nervous centres, but rather a series of
changes induced by the quantity and the
quality of the blood and by nervous impulses
from many quarters Thus the body works
as a whole. There is no autocratic centre ;
the most autocratic, the cerebrum itself, the
seat of what we term the will, comes under
the same law.

116. The pons consists mainly of great trans-
verse bands of fibres passing from one side of
the cerebellum to the other. In it there are
bundles of fibres passing upwards and down-
wards and masses of grey matter for some
of the roots of cranial nerves. The pons is
intimately related to the cerebellum, as the
transverse fibres form what are known as the
middle peduncles of that organ.

117. Immediately above the pons we find
the crura or peduncles of the brain, containing
the great motor and sensory paths. They
also contain numerous fibres connecting the
cerebellum with the cerebrum. Near the
peduncles we find four small bodies, the
corpora quadrigemina. These consist of layers

204 PRINCIPLES OF PHYSIOLOGY

of white and grey matter, showing a >char-
acteristic structure, and connected with the
fibres that come from the retinae of the eyes.
They are thus the first recipients of visual
impressions transmitted by the fibres of the
optic nerves These nervous impulses may
call forth contraction of the pupil, the round
aperture in the iris of the eye, or they may
excite more complex reflexes, along with the
action of the other ganglia in front of them,
the optic thalami and corpora striata. These
impulses, however, do not give rise to con-
sciousness. A sensation excited by impulses
coming from the eyes arises only when the
impulses are transmitted upwards from the
corpora quadrigemina to the visual centre in
the cerebrum. By the nervous arrangements,
also, the nasal and temporal halves of the
retinae are correlated to each other. Thus
all the fibres from the temporal side of each
retina pass to the corpus on the same side,
while those from the two nasal halves of the
retinae cross and reach the corpus on the other
side. Thus the right corpus receives impulses
from the temporal side of the right retina and

THE REGULATING MECHANISM 205

the nasal side of the left, while the left corpus
receives fibres from the left temporal and the
right nasal side. This secures single vision
with two eyes, if the image falls on correspond-
ing parts of the two retinae, as, for example, if
it falls on the right temporal and left nasal.
But if one image was formed on both temporal
or both nasal halves of the retina, there would
be double vision, as in squinting.

118. The optic thalami are sensory centres,
receiving impulses from below, and from them
impulses pass upwards to the cerebrum, where
they excite consciousness. They (a) may act,
however, as reflex mechanisms in conjunction
with the two masses immediately in front of
them, the corpora striata (b). These are motor
centres, receiving impulses from the motor
regions of the cortex of the cerebrum (c).
If a and b act together, without the influence
of c, there may be complicated reflex move-
ments, such as occur in the walking of the
somnambulist, or the unconscious perform-
ance of complicated movements.

119. The highest of all centres is the
cerebrum, consisting of two hemispheres, show-

206 PRINCIPLES OF PHYSIOLOGY

ing complicated convolutions. These convolu-
tions constitute an immense web of grey matter
showing numerous neurones of a peculiar
pyramidal form, arranged more or less in
layers. Numerous fibres pass in all directions
connecting one part of the cerebral mass with
the other. All the structural details indicate
co-ordination of function. Thus the convolu-
tions are connected by many associational
fibres ; fibres pass from the anterior to the
posterior parts of the cerebrum ; and numerous
fibres form the great transverse commissure,
known as the corpus callosum, which connects
one hemisphere with the other. Other smaller
transverse commissures exist. The cerebrum
receives nervous impulses from all parts of
the body. The sensory tracts in the cord
send numerous fibres upwards, and these reach
the grey matter of the cerebral convolu-
tions, in the posterior and lateral regions,
forming arborizations or networks near motor
neurones that lie in layers in the grey matter,
more especially in certain convolutions on
the lateral aspect of the cerebrum, From these
motor neurones fibres (axons) pass downwards

THE REGULATING MECHANISM 207

through the corpora striata into the peduncles
and then downwards in the pons and bulb
(where they cross or decussate) ; they then
pass down the anterior part of the cord,
until they reach the segment or segments
of the cord, in which they end by becom-
ing related to the great motor neurones
in the anterior part of the grey matter (see
p. 190). Fibres to and from the cerebrum are
related to the deep origins of the cranial
nerves. Finally, the cerebrum receives numer-
ous fibres from the cerebellum. The physio-
logical mechanism of the cerebrum is still
obscure. Portions of the grey matter of the
convolutions are concerned in the reception
of sensory impressions that are translated
into consciousness.

120. Definite districts of grey matter, more
especially in the posterior and lateral portions
of the cerebrum (temporo-sphenoidal convolu-
tions) receive messages that are translated
into sensations of touch, pressure, temperature,
vision, and hearing. These areas constitute
what are termed centres for the special senses.
No centre has been identified with taste.

208 PRINCIPLES OF PHYSIOLOGY

The olfactory bulbs and their roots are con-
nected with smell. In the middle region, on
each side of the great fissure known as the
Sylvian fissure, we find definite motor centres,
connected with the muscles and limbs and
with the muscles of the tongue and face on
the opposite side ; indeed it is highly probable
that every muscle of the body, even the laryn-
geal muscles associated with the production
of voice, has a centre in the cerebrum.
When these motor centres are irritated by
feeble electric shocks, movements of certain
muscles occur on the opposite side of the body.
Thus, stimulation of one centre, say on the
right side of the cerebrum, will cause a move-
ment of one of the muscles of the left hind leg.
Again, stimulation of another centre will
cause movement of the left fore leg. There
are complex centres for the lips, tongue, etc.
It must not be supposed, however, that these
motor centres are isolated or that they can
originate impulses. No doubt they are called
into action by nervous impulses of a sensory
character coming from other parts of the
cerebrum, or from below. Thus they also

THE REGULATING MECHANISM 209

constitute a reflex mechanism ; this appears
to be the general plan on which the whole
nervous system is constructed.

121. This fact is illustrated by associated
movements, such as those of speech or of the
hand in penmanship. A spoken word rouses
the auditory centre ; this transmits an impulse
to the motor centres of the speech mechanism ;
and the word may be audibly repeated. Or
the message from the auditory centre may
reach the centres for the ringers and arm of the
right hand and the word spoken may now be
written. Again, the sensory impressions may
come from the eye to the visual centre, and it
in turn may excite speech or the movements of
the ringers and hand. These impulses may
be also transmitted to parts of the cerebrum
and give rise to consciousness. Sometimes in
disease one of the links in this physiological
chain may be broken. A patient suffering
from some form of cerebral disease, when asked
the question, " What is your name ? " may be
unable to answer, not because he does not
hear (he is not deaf), but because he cannot
utter the words " John Smith " in response,

210 PRINCIPLES OF PHYSIOLOGY

as the route of the message from the auditory
centre to the speech centre has been inter-
rupted. If the physician writes the words,
" Is not your name John Smith ? " and puts
the paper before the patient's eyes, there is
the response : " Yes, certainly." Here the
message from the visual centre reaches the
speech centre, and the patient can utter his
name. Frequently also, a patient in certain
cerebral diseases may be perfectly conscious of
the name of a particular thing that he wants,
say a pencil, but he has forgotten the word
or uses a wrong one, to his own annoyance,
All this may be represented by diagrams, but
we must never forget that diagrams only
represent men's notions and that the real
mechanism may be something very different.
The functions of the anterior lobes of the cere-
bral hemispheres are unknown. Some have
supposed that in them we have the mechanism
for volition and the impulses that follow it.

122. The cerebellum is a regulating mechan-
ism. It may have other functions, but it
undoubtedly co-ordinates movements. By
co-ordination we mean that the time and

THE REGULATING MECHANISM 211

extent and order of a given group of muscular
contractions must be regulated to obtain a
required result. Thus in writing, many
muscles of the arm, fore-arm, and fingers act.
Again, in walking, complicated groups of
muscles must combine. It seems that in all
such mechanisms sensory impulses, or rather
impulses from the periphery, of which we may
or may not be conscious, start the mechanism.
Thus, in walking, impulses may come from the
skin of the feet and from the muscles and
tendons of the limb or from the eyes. If these
impulses reach the cerebrum, we may be
conscious of them. Without these impulses
even voluntary motion is irregular and ineffi-
cient. But many may find their way to
the back part of the cord and from it to the
cerebellum by what are called the inferior
peduncles of that body, which connect it
with the cord. The structure of the grey
matter of the cerebellum is extremely com-
plicated, and although many details are known
to histologists, we can form no conception of
its mechanism. But the grey matter shows
the usual plan of neurones of various forms, in

212 PRINCIPLES OF PHYSIOLOGY

layers. Round these neurones fibres that come
from below form arborizations. From these,
fibres proceed that find their way to the
cerebral hemisphere on the opposite side and
probably end in the motor centres. The
function of the cerebellum seems to be to
arrange these sensory impulses and to transmit
them to the special motor centre in the cortex
of the cerebrum, so as to bring about the
co-ordination that is necessary for the required
movement. Probably they do this by setting
into action motor centres for the movements
of special muscles. There is a faint analogy
in the card of a Jacquard loom, which so
arranges the threads as to enable the other
mechanisms to weave the desired pattern.
Finally, the cerebellum receives impulses
from the retina and from the internal ear,
and more especially from the semi-circular
canals of that organ. Such impressions from
these sense organs assist in the co-ordination
of movement, and in the maintenance of
equilibrium.

123. It cannot be too strongly emphasized
that our knowledge of the physiological

THE REGULATING MECHANISM 218

mechanism of the brain is still very imperfect.
When we examine under the microscope
sections that have been prepared by modern
methods, we are bewildered while we admire,
and there is often the involuntary exclama-
tion, " How does it all work ? "

CHAPTER XIII

RELATION TO THE OUTER AND INNER
WORLDS BY THE SENSES

124. WHEN we reflect on the physiological
nature of the senses, we find that the mind
becomes cognizant of two worlds from which
apparently come streams of feeling. There is
in the first place the inner world of our own
body in which there are physiological opera-
tions constantly going on, such as have been
indicated in the previous pages. Of some
of these operations we are more or less con-
scious, while many others, and probably by
far the greater number, never rise to the level
of consciousness even although nervous im-
pulses from many organs and tissues may reach
the higher centres. But we have what may be
termed internal senses, such as hunger and
thirst, satiety, the feeling of easy and com-
fortable respiration, as when we breathe fresh

214

THE OUTER AND INNER WORLDS 215

air, or have a feeling of the enjoyment of
life, such as one has in a state of health while
in the open air and in fine weather. As a
rule, we pay little attention to these internal
senses, which seem to be on the very thresh-
hold of feeling, but we are more or less con-
scious of them when they rise to a certain
intensity. Of many organs we are uncon-
scious, except when the nervous impulses
coming from them cause sensations that rise
to the level of pain. No doubt the nervous
centres are almost constantly receiving ner-
vous impulses which, although they may not
rise into the sphere of consciousness, yet fill
up, as it were, the interstices of our conscious
life and give it completeness. There do not
appear to be any special mechanisms for these
internal senses. The ordinary sensory or
centripetal nerves serve the purpose.

125. But we become cognizant of the outer
world by the five external senses of vision,
hearing, touch, taste, and smell, and we
learn about our position and movements in
the outer world by nervous impulses concerned
in what is called the muscular sense, and in the

216 PRINCIPLES OF PHYSIOLOGY

sense of equilibrium, and of the position
of the head in space. These external senses
have always a special mechanism, namely
(a) an end organ adapted for the reception of
a specific kind of stimulus ; (b) a nerve of
special sense ; and (c) an internal receptive
organ in the brain, which may act without
consciousness in reflexes, or with conscious
perception in the cerebrum. As an example
take the sense of vision. The normal stimulus
is light, the end organ is the retina, the nerve
is the optic nerve, the recipient centre is in
the first instance the corpora quadrigemina,
or optic lobes (as they are termed, for example,
in birds), and the centre of sensations of light
and colour are in the cerebrum, more especially
in a special area of grey matter.

126. The senses may be classified thus :
(a) Those in which the stimulus is movement
or pressures, namely — touch, hearing, the
muscular sense, and the sense of equilibrium ;
and (b) those in which the stimulus is more
of a molecular character, implying chemical
action, namely — vision, taste, and smell. In
the outer world, according to the conceptions

THE OUTER AND INNER WORLDS 217

of modern physics, matter is in a constant
state of movement, and we also assume the
movements of the ether as the cause of the
phenomena of heat, light, and electricity.
Such movements impinge on the body of an
animal of the simplest type, and by a slow
process of evolution through countless ages
sense organs and a nervous system have been
produced. Thus a pigmented spot has slowly
become an organ of vision, and a few special-
ized hairs have been developed into a recipient
organ for variations of pressure, a rudimentary
organ of touch or of hearing. As we ascend
the scale of animal life, the sense organs
become more and more complicated until we
find them as in man and in the higher animals.
Each sense organ, as already pointed out,
is adapted to its specific kind of stimulus.
Thus the retina is attuned to receive the
vibrations of light, and in the skin and in the
internal ear we have structures adapted for
receiving variations of pressure. These end
organs are composed, putting the matter in a
general way, of (a) modified epithelial cells
to protect and support ; (b) a highly special-

218 PRINCIPLES OF PHYSIOLOGY

ized form of nervous epithelium, which, in its
turn, is continued into neurones, and these
neurones ultimately, with probably inter-
mediary neurones, end in neurones in the
cerebrum. This is well seen in the retina,
where the specialized receptive epithelium
forms the remarkable layer of rods and cones
(Jacob's membrane) ; the rods and cones and
other structures of the retina are supported by
modified epithelium, forming structures called
the Mullerian fibres ; the layers of granules
in the retina and the layer of large multipolar
nerve cells constitute the neurones. From
these latter arise the fibres of the optic nerve,
which, as already pointed out, carry impulses
to the corpora quadrigemina, and thence to
he cerebrum.

127. The nerve of special sense is normally
stimulated by the end organ, but it may be
stimulated in other ways, as by pressure or
electric shock. Thus pressure on the eyeball
will give rise to dazzling impressions of light
(phosgenes). But the law is that in whatever
way the fibres of the nerve of special sense is
stimulated, the sensation is always of the

THE OUTER AND INNER WORLDS 219

same kind. Thus a luminous sensation always
follows stimulation of the optic nerve. When
it is divided by the surgeon, in removal of an
eyeball, if the patient is conscious, there is no
pain but the consciousness of a flash of light.
The same applies to all the other senses.
This law has been called the law of the
specific energy of the nerves of special sense,
but it does not imply that the nerve is anything
else than a conductor. The effect is due, as
has already been explained, to the arrange-
ments at the cerebral end of the nerve, by
which the messages are always translated into
sensations of the same kind.

128. Each sense organ works within certain
limits. Thus a stimulus may be so feeble as
not to produce an effect. This, as regards
intensity, is the threshold of sensation. The end-
organ is adapted to respond, say to vibrations,
within a certain range. Thus, if we look at
a spectrum the eye does not recognize light
or colour below the lower limit of the red, but
we know that there are vibrations in existence
that give rise to heat below the red end. The
skin may be affected by these low vibrations,

220 PRINCIPLES OF PHYSIOLOGY

but not the retina. As we pass upwards,
either by increasing the intensity or, as in
viewing a spectrum, by increasing the number
of vibrations, sensation continues, and it may
vary in intensity, or in quality, or in both.

129. The relation between the strength of
the stimulus applied to an organ of sense and
the intensity of the sensation has been investi-
gated. It is found that the intensity of the
sensation increases with an increase in the
strength of the stimulus, but in a peculiar way.
It is not in direct proportion. For example,
doubling or trebling the strength of the stimu-
lus does not double or treble the intensity of
the sensation, but the latter increases by
smaller and smaller increments until no
difference in the intensity of the sensation
can be observed. Thus, in a very intense
light the additional light of a candle may not
be perceived Refinements of this law have
been studied, but the general principle is as
above stated. It is evident that there is
thus a protective action against injury from
excessive stimulation.

130. With regard to vibrations, a sensation

THE OUTER AND INNER WORLDS 221

arises when they reach a certain number,
and it changes as they increase. This, as
already pointed out, is well seen in a
spectrum. Proceeding from the low red
upwards we pass through the various colours,
red, orange, yellow, green, blue, indigo and
violet. The range is an octave, that is
to say, the number of vibrations producing
violet are about double the number required
for red. With the sense of hearing, the first
tone audible as a musical tone is produced by
about thirty-three vibrations per second, while
the highest audible tone corresponds to a little
over thirty thousand per second. Thus the
ear has in most individuals a range of about
eleven octaves. Beyond the highest audible
sound, there are however many vibrations
which make no impression on the human
ear, just as there are numerous vibrations
beyond the upper limit of the violet of the
spectrum, known to physicists, such as the
Rontgen rays. These have no effect on the
human retina, and yet their existence has
been proved by special methods of research.
It is possible, even probable, that some

222 PRINCIPLES OF PHYSIOLOGY

animals may hear sounds that are inaudible
to man. Our knowledge, therefore, of the
external world is limited by our senses, and
there may be many phenomena for which
we have no powers of perception. For
example, we have no organ for the perception
of changes in the electrical condition of sur-
rounding matter, and were we supplied with
such an organ a new world would be opened
up.

131. The delicacy of the sense organs is
remarkable. Thus we may detect a pressure
on the skin of -002 gram. We can detect the
eighth of a degree centigrade when the
temperature of the skin is 18° C. The
shortening of a muscle may be detected so
small as -004 of a millimetre (l-6,000th of an
inch). The ear can detect vibrations of sound
caused by movements of molecules of the air
of -0004 mm. (the 1-600, 000th of an inch, or
1-1 Oth of the wave length of green light ;
while the retina is even more sensitive ; — the
energy of the feeblest light that can be dis-
tinguished at a certain distance, say 100
yards, is of the same order of magnitude as

THE OUTER AND INNER WORLDS 223

that of the feeblest tone that can be heard by
the ear at the same distance ; one part of sul-
phate of quinine can be detected in 1,000.000
of water ; the odour of one part of bromine,
and even much less of iodoform may be de-
tected in 1,000,000 of air. Possibly the senses
of some animals are even more delicate.

132. Each organ of sense has accessory
apparatus suitable to it. Thus the eyeball is
a camera for the purpose of forming, in accord-
ance with the laws of dioptrics, an image on
the retina. Vibrations of sound are conveyed
to the internal ear by a complicated conducting
mechanism of a drumhead, a chain of bones,
and reach a delicate organ in the cochlea,
known as the organ of Corti. By hair-like
processes in the semi- circular canals of the
inner ear, acted on by pressures of fluid in the
canals, varying according to the position
of the head, we appreciate the position of
the head in space, and we regulate the move-
ments of the body accordingly. In the
tongue and nose there are special epithelial
structures, such as the taste bodies and the
olfactory epithelium acted on by odoriferous

224 PRINCIPLES OF PHYSIOLOGY

particles. In the skin there are plexuses of
fine nerve fibres, running even among the
cells of the epidermis, which receive delicate
pressures, as in touch. These pressures are
also detected by nerve fibres connected with
specialized structures formed mainly of epider-
mic cells, such as touch bodies, tactile cor-
puscles, and Paccinian bodies. No special
terminal organs for temperature have been
discovered in the skin, but there are points in
the skin sensitive to heat, others to cold, and
both distinguishable from those devoted to
pressure. It would seem there are also pain
spots. There appear to be even different
systems of sensibility in the skin. If a sensory
nerve to an area of skin is divided, sensibility
may return if the ends unite. The sensations
that return first have been termed prolo-
pathic, and depend on heat, cold, and pain
spots. But another order of sensations return
later, and seem to depend on tactile sensations
and a finer sense of sensibility to pain. This
kind of sensibility has been called epicritic.
It follows, then, that when we bring the
finger flat against a surface we stimulate

THE OUTER AND INNER WORLDS 225

a complicated mechanism giving rise to
different kinds of sensations. In recent years
it has been more and more clearly shown
that in all the terminal organs of the senses
there is differentiation to a degree at one time
unsuspected.

133. It is important also to observe that
there seems to be no correspondence between
the physical nature of the stimulus and the
sensation. They are absolutely unlike. We
have acquired knowledge of the various stimuli,
say light or sound, by observation, experiment,
hypothesis and theory, but there is no simi-
larity between certain wave lengths of the
ether and a sensation of violet, nor between the
varying pressure of a wave in the air and the
sensation of a musical tone. The sound of an
orchestra may be represented mathematically
by a curve, and physically by variations in air
pressures, but the psychical effect is quite a
different thing. We pass at this point from
the region of the physical and physiological
(both may ultimately be the same) into the
still more occult region of the psychical.

CHAPTER XIV

THE VOICE

134. THE human voice is produced by the
vibrations of the margins of two ligaments in
the larynx called the vocal cords. Voice
should be distinguished from speech. Many of
the lower animals have voice, but none have
the faculty of speech in the same sense as we
find it in man. There may be speech with-
out voice as in whispering, while in singing a
musical scale we have voice without speech.

135. The apparatus for the production of
voice consists of (a) a wind chest, the thorax,
by means of which a blast of air may be forced
from the lungs through the windpipe or
trachea to the larynx ; (b) a sound box, the
larynx, containing the vocal cords ; and (c)
the throat, mouth, and nasal, and other pas-
sages that modify the sound produced in the

larynx. Voice is almost invariably produced
226

THE VOICE 227

during expiration, but sounds may also be
produced by inspiratory efforts. The larynx
is formed of cartilages connected by ligaments
and more or less capable of being moved on
each other by muscles, the muscles of the
larynx. The chief cartilages are the thyroid
or shield forming the prominence known as
Adam's apple. Immediately below it is the
cricoid or ring cartilage, shaped somewhat
like a signet ring, with the signet directed to
the back. On the signet there rest two small
cartilages, the arytenoids. These are pyra-
midal in shape, the bases of the two pyramids
resting on the signet of the cricoid while the
apices are directed upwards. The true vocal
cords are two membranes or ligaments stretched
from the base of each arytenoid forwards to
the thyroid. They are formed of connective
tissue fibres, with which are intermingled
many fibres of elastic tissue. Running in
the larynx from before backwards they leave
a narrow chink between their free edges
called the glottis. During calm inspiration
the glottis is widely opened, but on the
approach of an expiration the free margins

228 PRINCIPLES OF PHYSIOLOGY

of the cords come closer together and the
glottis becomes much narrower. If voice is
now to be produced, as when a note is sung,
the margins touch and the glottis is entirely
closed for an instant. The pressure of the
air below the cords is increased by the expira-
tory effort, and there is a puff of air sent out
between the margins of the cords. This
relieves the pressure and instantly again the
glottis is closed by the elasticity of the cords.
Again the pressure rises and there is another
puff and so on, and the margins of the cords
thus move with each puff ; in other words, they
vibrate. So that the organ of voice is on the
principle of the siren, an acoustical instru-
ment by which musical tones are produced
by the fusion of individual puffs of air.

136. The vocal cords can be tightened or
relaxed, and their free margins can be separ-
ated or approximated by the action of special
muscles. Thus, in singing a scale, beginning
with the low note, the cords are gradually
tightened by two muscles, the crico-thyroids,
passing from the sides of the signet of the
cricord upwards and forwards to the thyroid.

THE VOICE 229

These muscles, when they contract, put the
vocal cords on the stretch, and the stretch
increases as the pitch of the note rises. If we
remember that the true vocal cords pass
forward from the arytenoids to the thyroid, and
if we suppose that each arytenoid is capable of
rotating round a vertical axis passing from the
apex of the pyramid to its base, we can under-
stand how the glottis is opened and closed. Two
small muscles, the posterior crico- arytenoids^
pass from the signet of the cricoid to the outer
angles of the base of the arytenoids, and when
they contract they so rotate the arytenoids
as to carry outwards the cords and thus they
enlarge the aperture of the glottis. Their
antagonists are a pair of small muscles, the
lateral crico- arytenoids, which pass backwards
from the sides of the cricoid to the outer
angles of the arytenoids. When these con-
tract they pull the angle forwards and inwards,
and thus approximate the cords. By these
simple mechanisms the position and tension of
the cords is controlled. The amplitude of
movement of each muscle is only a very
small fraction of an inch, and yet a soprano

280 PRINCIPLES OF PHYSIOLOGY

vocalist can produce a trill with the greatest
distinctness.

137. When we listen to musical tones
emitted by the human voice we notice varia-
tions of pitch, loudness or intensity, and
quality. Pitch depends on the number of
vibrations executed by the cords in a given
time, or, more correctly, on the duration of
each vibration. Thus in singing a note,
say the middle C of the piano, the cords
vibrate about 256 times per second. Each
vibration therefore lasts the 1-256 of a
second. The greater the number of vibra-
tions in a given time the higher the pitch.
The range of the human voice is about three
octaves — from fa|; (87 vibrations per second),
to sol fcj (768). In men the vocal cords are
more elongated than in women in the ratio of
3 : 2, so that the male voice is of lower pitch.
At the age of puberty, the larynx grows rapidly
and the voice of the boy " breaks " in conse-
quence of the lengthening of the cords, and it
generally falls about an octave in pitch. The
highest pitch reached by the human voice is
recorded of Lucrezia Agujari, who was heard

THE VOICE 281

by Mozart to sing c in alt, three octaves above
middle c (2,048 vibrations), while the lowest
is that of Gaspard Forster, who gave a note
nearly three octaves below the middle c (42
vibrations). Musical sounds begin with about
32 vibrations per second. These two voices,
therefore, had a range of about six octaves,
but the usual range between the lowest bass
and the highest soprano of ordinary voices
is three octaves. The human ear passes
in range from 32 to 33,768 vibrations per sec-
ond, or about eleven octaves, and it is inter-
esting to notice that the range of the human
voice occupies about the middle of that vast
range. It is said that some have been able
to hear tones produced by 40,000 vibrations
per second. The tone of the 32-foot organ
pipe is produced by about 32 vibrations per
second, while the highest tone of the organ,
that of the piccolo stop, is produced by about
4,000 vibrations per second. With reference
to these figures it is interesting to compare
the range of the human voice.

138. Loudness or intensity depends on the
amplitude of the vibrations of the cords — the

232 PRINCIPLES OF PHYSIOLOGY

greater the amplitude, or extent of move-
ment, the louder the tone. This will be
largely determined, not so much by the force
of the current of air from the lungs as by
the degree of elasticity of the cords.

139. The quality or timbre of the voice
depends on the same laws as determine the
quality of musical instruments. The tone
produced by the vibrations of the cords is a
compound tone depending on a fundamental
tone which gives the pitch, with which are
combined many partials or overtones, which,
as regards the number of their vibrations, are
simple multiples of the frequency of the
fundamental. Thus, if the fundamental tone
is produced by, say, 100 vibrations per
second, then the partials are in the order of
1, 2, 3, etc. ; that is, the first partial corresponds
to 200 vibrations per second, the second to
300, and so on. The cavities above the cords,
such as the space immediately above the
cords and below the so-called false cords, the
cavity of the pharynx, nasal passages, sinuses
in the bones of the face, and the mouth, all
act as resonance chambers. These develop,

THE VOICE 233

by resonance, a selection of the overtones,
and thus give quality to the voice. A very
small change in the capacity of these
chambers will alter the quality.

140. Speech is the expression of ideas by
means of the voice or by the breath (without
voice), as in whispering. Speech sounds are
produced by the articulating mechanism.
Certain open sounds, more or less modified,
give the vowels, which are musical tones.
So-called consonants are produced in many
ways, but these cannot be here discussed.
The simplest view to take of them is that
they are breaks of, or interferences with, the
current of air which, if the mouth were open,
and the articulating mechanism were at rest,
would produce vowel tones. Physiologically
all words are made up of certain sounds
that may be called phones. Each phone may
have its own pitch, intensity, and quality ;
and by their blending a word is produced.
Each phone on a gramophone record is
composed of curves that vary as to number
(pitch), amplitude (loudness) and form (qual-
ity), consequently when the vibratory needle

234 PRINCIPLES OF PHYSIOLOGY

again runs over these curves, the sound
must be reproduced. Nature knows nothing
of letters and syllables ; words are either
simple phones or combinations of phones,
and each phone is formed of vibrations. This
is nature's longhand method of recording
speech : written or printed letters and sylla-
bles are a species of shorthand invented by
man.

CHAPTER XV

DEATH

141. DURING the earlier years of life and up
to the period of adolescence, the body increases
in size and weight. The processes of growth
are in excess of those of waste. After adoles-
cence, the body may remain for many years
without much variation in bulk and weight ;
but even before middle life signs of decay and
degeneration are noticeable, especially in cer-
tain organs. Grey hairs appear, the teeth decay,
there may be a diminution in the elasticity
of parts and in the power of the muscles, and
there may be slow changes in some of the
internal organs that are still compatible with
ordinary health. In advanced life these
changes become more apparent. Some have
supposed that such changes may be due
to the action of poisonous substances, formed

mainly in the alimentary canal, and even the
235

236 PRINCIPLES OF PHYSIOLOGY

phagocytic action of the colourless cells of
the blood has been invoked, but there is no
clear evidence in support of these views.
In old age there is a gradual process of
degeneration more or less of all the tissues —
the nervous tissues suffer least and last. It is
not easy to understand why there should be
this tendency to degeneration, and conceiv-
ably, in perfect hygienic circumstances, and
with an absolutely clean pedigree, such de-
generation might not occur. Early death
should only be caused by accident. In an
ideal physiological life, death should come
late as a result of gradually increasing weak-
ness without pain or suffering, and it should
be a process as normal as going to sleep. In
most instances, however, degenerative changes
do not affect all the organs alike. Some, such
as the heart, or lungs, or kidneys, probably
on account of an error in the mode of life, or
a want of adaptability to the environment,
may undergo changes that unfit them for
their work. This disturbs the physiological
balance and there may be suffering ending
in death. When this occurs, the mechanism

DEATH 237

of the heart or of breathing, or of the nervous
system, may break down, and death of the
body as a whole takes place. The organs,
or rather, the tissues in the organs, the cells,
the living matter, die more slowly, and at
last these too cease to live The organic
matter of the body then, under the influence
of micro-organisms in the air or the soil,
breaks down by processes of putrefaction,
and, in course of time, it is decomposed
into simpler and simpler organic substances
until the ultimate elements are reached. Thus
organic matter becomes again inorganic.

142. The causes of longevity are not under-
stood ; nor, as already mentioned, is it evident
why the degenerative changes above referred
to should come on. Each species of animal,
at all events among the higher animals,
seems to be so constructed as to have a
longevity peculiar to the species. Attempts
have been made to connect this in some
way with the period of utero-gestation, but
little reliance can be placed on such specu-
lations. It is clear, however, that longevity
is largely a matter of heredity, if accidents

238 PRINCIPLES OF PHYSIOLOGY

of all kinds are avoided. The contraction of
a pneumonia or of a fever in early life may be
regarded as an accident which has cut short
the normal duration of life.

CHAPTER XVI

PHILOSOPHICAL QUESTIONS AND THE
TREND OF PHYSIOLOGY

143. IN the brief survey we have given of
physiological processes, questions of a philo-
sophical nature cannot have failed to occur
to the mind. There is one always keenly
debated, namely, the existence of a vital force
or energy, as distinguished from the physical
forces with which we are acquainted. It does
not serve any practical purpose either to
deny or to affirm the existence of such a
force. As a matter of fact, we are met every-
where with phenomena which cannot be
explained by our present knowledge of physi-
cal and chemical science. Numerous in-
stances of such phenomena have been pointed
out, and it is surely scientific and philosophical
to recognize the limits of our knowledge. With
the progress of science we may, and indeed

239

240 PRINCIPLES OF PHYSIOLOGY

will, get further into the molecular arena, and
be able to explain some of those phenomena,
which at present are so obscure. We need
not proclaim what we do not know, and assert
that all of these phenomena are in reality
physical, because this is simply begging the
question. There are phenomena, however,
which we may feel assured can never be so
explained. Those of a mental kind can never
be thus accounted for, and no metaphysical
subtleties, either from a materialistic or an
idealistic standpoint, will ever satisfy the
mind. How are we to give a physiological
explanation of human personality ?

144. Progress in physiology can only be
made by a resolute investigation of all the vital,
physical, and chemical phenomena that occur
in living matter and in living beings. This must
be done by the methods followed by physiolo-
gists, with all the help they can receive from
the rapid accumulation of knowledge. At one
time anatomical, at other times histological,
considerations govern the science. The older
anatomists were content to display the organs
and to infer their functions. The cell theory

PHILOSOPHICAL REFLECTIONS 241

and the genesis of tissues (not a hundred years
old) at one time seemed to be the key to an
explanation oi ital phenomena. Then came
a time, not so long ago, when physical methods
of investigation were in vogue, and it was
thought that many phenomena were merely
physical, requiring for their interpretation
measurement, weighing, and graphic registra-
tion. At the present time, considerations of
chemical phenomena are prevalent in the
minds of physiologists. The structure of the
complex proteins and other bodies is being
investigated ; syntheses of many organic sub-
stances have been accomplished ; even elemen-
tary protein-like bodies have been formed,
and the formation of complicated proteins is
within sight. Chemical phenomena in the
great processes of respiration, nutrition, and
digestion are being thoroughly investigated.
The agency of ferments is now recognized as
all-important not only in digestion but in
nutrition. Osmotic phenomena in living
matter have received recently much attention,
and some of the visions of advanced physicists
as to the constitution of matter have been
9

242 PRINCIPLES OF PHYSIOLOGY

applied tentatively to the explanation of
physiological processes. The result is remark-
able. On all hands it is admitted that the
phenomena in living matter are much more
complex than they were at one time thought
to be, and everywhere we are brought face to
face with vital conditions which modify the
physical phenomena, and which, at present,
refuse to be explained. One may be sure that
a century hence advanced mathematicians,
chemists and physicists (the physiologists of
their day) will still be working at the problems
of physiology.

BIBLIOGRAPHY

General Biology.

MoKendrick : Text Book of Physiology, vol. I., chapters
1, 2 and 3.

Luciani : Human Physiology, vol. I., Introduction and
chapters 1, 2 and 3.

Herbert Spencer : Principles of Biology, voL I., part 2,
chapters 1-6.

J. Theodore Merz, History of European Thought, vol.

II., chapters 8, 9, 10 and 11,
Energy.

Clerk Maxwell : Matter and Motion.

Tait : Recent Advance in Physical Science.

Hermann : Translated by Gamgee : Human Physiology.

Helmholtz : Lectures on Scientific Subjects, No. 7.

Grove : Correlation of Physical Forces.
TheCeU.

E. B. Wilson : The Cell in Development and Inheritance
Heredity.

J. Arthur Thomson : Heredity, chapters 1 and 2.
Development.

Thomas Bryoe : Quain's Anatomy, vol. I., section 1.
General Physiology.

Halliburton's Handbook of Physiology.
The Nervous System and Senses.

(1) Nerves : Gotch, in Schafer's Handbook of Physiology,
vol. II., page 45L

(2) Nerve cell : Schafer, op. cit., vol. II., page 592.

(3) Cerebral cortex : Schafer, op. cit., voL II., page 697.

(4) Sympathetic. Langley, in Schafer, ap. cit., vol. II.,
page 616.

(5) Spinal cord and medulla : Sherringtoo, in Schafer, op.
cit., vol. I., pages 783, 784.

243

244 PRINCIPLES OF PHYSIOLOGY

The Senses.

McKendrick & Snodgrass, The Senses.
Greenwood : Physiology of Special Senses.
McKendrick : Text- Book, vol. II., especially Hearing.

Philosophical.

Dastre : Life and Death.

F. Czapek : Chemical Phenomena in Life.

GLOSSARY

Abiogenesis (Greek, a, privative ; bios, life ; genesis,

production). — Spontaneous generation.
Accelerator nerves (Latin, accelero, to hasten). — Nerves

which, when stimulated, quicken the rate of the

heart's action.

Adrenals. — The supra-renal capsules.
Adsorption (Latin ad, to, sorbere, to suck). — The attraction

of gelatin, etc., for certain substances ; not solution.
Afferent (Latin affere, to convey to). Conveying towards,
Afterbirth. — The placenta.
Agglutination (Latin, agglutinarey to cement to). — The

gathering together into small masses of bacteria.
Anaesthesia (Greek, a, privative; aisthesis, perception). —

Loss of sensation.
Anion. — An electro-negative body that passes to the

positive pole during passage of a current.
Anode (Greek, ana, upwards ; odos, a way). — The positive

pole of a battery.
Argon (Greek, argos, inactive), a recently discovered

element.
Assimilation (Latin, assimilare, to make like). — Conversion

of foodstuffs into living matter.
Axilla. — The armpit.
Axis cylinder. — The central filament in a nerve fibre.

Bacillus (Latin, bacillum, a little rod). — Bacilli are micro-
organisms.

Bacteria (Greek, bacterion, a rod). — Unicellular micro-
organisms having no chlorophyll.

Basement Membrane. — A delicate membrane on mucou*
and serous surfaces, bearing epithelium.
245

246 PRINCIPLES OF PHYSIOLOGY

Blastoderm (Greek, blastano, germinate; derma, skin) —
A layer of cells formed by repeated division of the
primitive cells.

Brownian movement. — Rapid motion of minute micro-
scopical particles, first described by R. Brown,
botanist.

Brunner's Glands. — Small racemose (grape -like) glands
found in the duodenum.

Calorimeter. — An apparatus for measuring the heat of

combustion.
Calorie. — Thermal unit.
Cartilage. — Gristle.
Casein. — A proteid, forming chief constituent of cheese.

Formed from caseinogen, by action of acids or rennin.
Cathode, or Katode. — Negative pole of a battery.
Cation, or Ration (Greek, katon, that which goes down). —

An electro-positive body that passes to the negative

pole during the passage of a current.
Centrosome. — A minute body found within a cell.
Chemiotaxis (Greek, chemia, chemistry ; taxis, order). —

A property of attraction drawing micro-organisms

or their products to the white corpuscles of the blood.
Chondrin. — A proteid found in cartilage, etc.
Chromatin (Greek, chroma, colour). — Colourable matter

found in the nuclei of cells.
Chyle (Greek, chylos, juice). — A milk-like fluid absorbed

by the lacteal vessels in the villi of the small intestine.
Chyme (Greek, chymos, juice). — Semi-digested matter

that passes from the stomach into the duodenum.
Coagulation (Latin, con, agere, to drive together). — The

formation of a blood clot.
Colloids (Greek, kolla, glue or jelly). — Non-crystallizable

matter that does not pass through an animal mem-
brane in ordinary circumstances.
Corpus, corpora. — Bodies, such as corpora quadrigemina,

four twin-like bodies.
Crystalloids. — Substances that in dialysis pass through

animal membranes.

GLOSSARY 247

Cutis vera. — The true skin.

Cytoblastema (Greek, Tcutos, a cell ; blastema, growth). —

Cell protoplasm. Cytoplasm, protoplasmic matter

of a cell.

Defensive bodies. — Substances in the blood that tend to
destroy micro-organisms. (Germicidal, germ-destroy-
ing-)

Deglutition. — Act of swallowing.

Deliquescent. — Melting away by absorption of water.

Derma,— The skin.

Dialysis (Greek, dialusis, a loosening). — Separation of
substances by means of an animal membrane.

Diaphragm. — Midriff, a membrane-muscular partition
between thorax and abdomen.

Dissociation. — Splitting up of compounds without chemical
change.

Duodenum (Latin, duodeni, twelve). — The first portion of
the small intestine.

Ectoderm, Endoderm (Greek, ektos, outward; endon,

inward). — Two layers of the early embryo. Ecto-
derm is sometimes termed the epiblast, and the endo-

derm, the hypoblast.
Elastic tissue. — Yellow fibrous tissue, found in certain

ligaments.
Emulsion (Latin, emulgere, to milk out). — A special kind

of mixture of various substances (see text).
Endosmose (Greek, endon, within ; osmosis, impulsion). —

The passing of a fluid through an animal membrane

from a rarer into a denser fluid.
Enzymes. — Chemical substances secreted by living cells

or by micro-organisms which act catalytically.

Sometimes termed ferments.
Epidermis (Greek, epi, upon ; derma, the skin). — The

superficial layer of the skin, covering the dermis, or

cutis vera, the true skin.
Epiglottis (Greek, epi, upon; glottis, glottis). — A fibro-

cartilage in front of the glottis to protect the opening

into the larynx.

248 PRINCIPLES OF PHYSIOLOGY

Epithelium (Greek, epithemi, to place upon). — A layer or

layers of cells on a basement membrane.
Erythrodextrin and achroodextrin are dextrins formed from

starch by the action of saliva. The first passes into

sugar.

Excretion (Latin, excernere, to separate from).
Fallopian Tubes. — Ducts passing from the ovary to the

uterus,
Fecundation (Latin, fecundare, to make fruitful). — The

blending of the male and female elements.
Fermentation (Latin, fervere, to boil). — Changes in certain

matters caused by enzymes or micro-organisms.
Fibrin (Latin, fibra, a fibre). — The fibrous element in

blood clot.
Fibrinogen (fibrin and, Greek, gennao, to produce). — The

substance in blood from which fibrin is formed.

Fibrinoplastin, a globulin in blood.
Ganglion (Greek, ganglion, a tumour). — A nodule of

nervous matter, forming a nerve centre. In it are

found nerve-fibres, nerve cells, and supporting tissue.
Gelatin (Latin, gelu, frost). — A proteid found in white

fibrous and other tissue.
Glycogen (Greek, glucus, sweet ; gennao, to produce). —

Animal starch, formed chiefly in the liver.
Haem-, Haema-, Haemato. — Terms applied to substances

derived from blood, such as Haemalin, Haematoidin.
Haemoglobin. — The colouring matter of the blood.
Haemolysins. — Substances that dissolve red blood cells.
Haematoblasts. — Small bodies in blood, or blood plates.
Histology (Greek, histos, a web ; logos, an account). — The

structure of the tissues.

Hormones (Greek, hormao, to arouse). — Chemical sub-
stances formed in epithelium which excite the secre-
tion of glands.
Hyperaesthesia (Greek, huper, above ; aisthesis, sensation).

— Excessive sensibility.
Hypertrophy (Greek, huper, in excess ; trophe, nutrition). —

Excess of nutrition.

GLOSSARY 249

Imbibition (Latin, imbibere, to drink in). — The passage of

fluid into dead or living tissues.
Inhibition (Latin, inhibeo, to restrain). — Arrest of function

of a nerve centre.
Inosite (Greek, is, inos, muscle). — A kind of sugar found

in muscle.
Ions. — The dissociation of molecules into elements or

ions, a name given to the elements of a liquid set free

by the passage through it of an electric current

(electrolysis). Ions set free at the anode are anions ;

those at the katode, kations.
Irritability (Latin, irritare, to provoke). — The property of

living matter by which it is affected by a stimulus.

Jejunum (Latin, jejunus, hungry). — Upper two-fifths of
small intestine.

Karyokinesis (Greek, karuon, nucleus ; kineo, to move). —
The changes that occur in a nucleus in connection
with cell division.

Keratin (Greek, keras, horn). — A substance found in hairs,
nails, and other epidermic tissues,

Laevulose (Latin, laevus, left). — One of the substances
formed from cane sugar by the enzyme invertase.-
The other substance is dextrose.

Lysis (Greek, lusis, solution). — Occurs in many words, such
as ana-lysis, para-lysis, etc.

Macula germinative. — The germinal spot in the ovum.

Malpighian corpuscles. — Small bodies in the cortex of the
kidney consisting of a plexus of capillaries, forming
a ball, which is surrounded by the beginning of a
uriniferous tubule (the capsule). Malpighian glome-
ruli, in the spleen.

Me* (Greek, middle) ; mes-enteric (Greek, enteron). —
Glands : small lymphatic glands found in the mesen-
tery ; the membrane which connects the small
intestine with the posterior wall of the abdomen (a
reflection of the peritoneum).

250 PRINCIPLES OF PHYSIOLOGY

Morphology (Greek, morphe, form ; logos, an account). —
The science that investigates the laws of form and
arrangement of parts of the bodies of plants and
animals.

Myosin (Greek, mus, muscle). — A globulin found in
muscle.

Myxoedema (Greek, muxa, mucus ; oedema, a swelling). —
A disease in which the thyroid body is atrophied and
the connective tissues of the body are infiltrated
with a mucus-like matter.

Neuron. — A nerve cell. See text.

Nuclein. — A complicated chemical substance containing
phosphorus, found in nuclei.

Nucleus. — A kernel, a body found in cells.

Oesophagus (Greek, oisophagos, oio, oiso, to carry ; phago,
to eat). — The carrier of food, the gullet.

Ontogenesis (Greek, onta, things ; genesis, creation). — The
history of the development of the individual.

Pepsin (Greek, pepio, to digest). — The enzyme of the
gastric juice.

Periosteum (Greek, periosteos, around the bones). — The
connective tissue covering of the bones.

Pharynx (Greek, pharungx, the throat). — The musculo-
membranous bag or cavity leading into the gullet.

Placenta.— The afterbirth.

Protein (Greek, proteno, to be in the first place). — A sub-
stance containing carbon, hydrogen, oxygen, and
nitrogen. Ex. : Albumen (white) of egg.

Proteolysis. — The decomposition of proteins.

Protoplasm (Greek, protos, first ; plasma, something
formed or moulded). — See text.

Ptyalin (Greek, ptualon, saliva). — The enzyme of saliva.

Pylorus (Greek, pule, a gate ; ora, care). — A gate-keeper.
The passage leading from the stomach into the
duodenum.

Racemose (Latin, racemus, bunch of grapes). — A special
form of gland with branching ducts and acini or
pouches, at the termination of the smallest ducts*

GLOSSARY 251

Rectum (Latin, rectus, straight). — The last part of the
bowel terminating at the anus.

Rennin. — The enzyme found in the fourth stomach of
ruminants, and in the gastric juice of young mammals.

Rods and cones. — Structures in the external layer of the
retina.

Rods of Corti. — Specialized epithelium in the scala inter-
media of the cochlea.

Schizomycetes (Greek, schizo, to split; mukes, mukatos,
a mushroom). — Split fungi multiplying by fission.

Secretin. — A substance in the duodenum which, by
absorption into the blood, stimulates the pancreas to
secrete.

Sero-therapy. — The injection of specially prepared blood
serum in the treatment of various diseases.

Skatol (Greek, skas, skatos, dung). — A substance in faeces
arising from decomposition of proteids.

Spermatoblast (Greek, sperma, semen ; blastano, to germi-
nate).— Cells that form spermatozoa.

Spermatozoa (Greek, sperma, semen ; zoon, an animal).

Thymus (Greek, thumos, an onion). — A blood gland of
early life found behind the breast bone.

Thyro (Greek, thureos, a shield). — Applied to thyroid
cartilage of larynx, and the thyroid body.

Trophoblast (Greek, tropheo, to nourish ; blastos, a germ). —
A portion of the epiblastic layers of the embryo that
has to do with the formation of the placenta.

Urea (Greek, uron, uron). — A crystalline substance found
in the urine. Uric acid. See text.

Vaso-motor. — Term applied to nerves that govern the
smaller arterioles.

HISTORICAL NOTES

GREAT PHYSIOLOGISTS

1500— Achillini, 1461-1512. Release of anatomy from

the influence of Galen. Practice of dissection.
1530 — Vesalius, 1514-1564. Anatomy of heart and

vessels.
1540— Falloposis, 1528-1562. Colombus, died 1559.

Circulation valves.

1550— Eustachius, 1520-1574. Vessels, etc., Anatomist.
Servetus, 1509-1553. Discovery of pulmonary

circulation*

1560 — Fabricius al aquapendente, 1537-1619. Vessels.
1580 — Caesalpinus, 1519-1603. Anatomist. Forerunner

of Harvey.
1610— William Harvey, 1578-1657. Circulation of the

blood. De motu cordis et sanguinis, published

1628.

1620 — Asselli, about 1622. Discovery of the lacteaU.
1640— Borelli, 1608-1679. Animal motion. The heart.
1650 — Pecquet, about 1621. Discovery of thoracic duct.

Boyle, 1627-1691. Laws of gases.
1660 — Malpighi, 1628-1694. Discovery of capillaries.
1670 — Leeuwenhoek. Microscopical investigations.
Hooke, 1635-1702. Theory of respiration.
Mayow, 1645-1679. Theory of respiration.
1680— Ruysch, 1638-1731. Art of injecting vessels.
1700 — Boerhaave, 1668-1738. General physiology.
1710— Stephen Hales, 1677-1761. Hydraulics of the

circulation.

Morgagni, 1682-1771. Beginning of pathology.
1740— Haller, 1708-1777. Theory of muscular irritability.
252

HISTORICAL NOTES 253

1760— John Hunter, 1728-1793. Action of vessels, etc.
Spallanzani, 1729-1799. Digestive process, respira-
tion, generation.

Galvani, 1737-1798. Animal electricity.
Hewson, 1719-1774. Functions of blood glands.
1770— Volta, 1745-1826. Electricity.

Lamarck, 1744-1829. Theory of development.
1780— Gall, 1758-1828. Dissection of brain.
1790 — Humphry Davy, about 1799. Gases from blood.
1800 — Thomas Young, 1773-1820. Measurement of time,

theory of colour, hydraulics of circulation.
Charles Bell, 1774-1842. Functions of nerves.
1810— Majendie, 1783-1855. Theory of absorption.
1820 — Beaumont, about 1824. Gastric digestion in man.
Gemelin, 1788-1853. Animal chemistry.
E. H. Weber, 1795-1878. Circulation, muscular

action, senses.

Marshall Hall, 1790-1857. Reflex actions.
Flourens, 1794-1867. Central nervous system.
Poiseuille, 1799-1869. Circulation.
1830 — Johann Muller, 1801-1855. General physiology.
Great handbook. Foundation of modern Ger-
man school of physiologists.
Schleiden, 1804-1872. Cell theory.
Mattencei, 1811-1869. Electro-physiology.
Magnus, about 1836. Analysis of gases of blood.
1840— Claude Bernard, 1813-1878. Vaso-motor nerves,

glycogenic function, etc.
John Goodsir, 1814-1867. Secretion, etc.
Fechner, 1801-1887. Psychophysical actions.
Darwin, 1809-1882. " Origin of Species," 1859.
Andrew Buchanan, 1798-1882. Coagulation of

blood.
1850— Ludwig, 1816-1895. Hydraulics of circulation.

Hermann Helmholtz, 1812-1894. Muscle — rate of
nerve impulse, hearing, vision, application of
physical methods of research,
Donders, 1818-1890. Vision.

254 PRINCIPLES OF PHYSIOLOGY

Du Bois Raymond, 1 8 1 8 - 1 896. Electro-physiology.

Lister, 1827-1912. Blood-ooagulation, micro-
organisms, aseptic methods in surgery.
More recent physiologists, chiefly British, whose
writings are readily available :

1. Wooldridge, Halliburton, Hammarston, Fischer (syn-

theses of proteid-like bodies).

2. Electro-physiology. — Hermann, Kronecker, Burdon-

Sanderson, Waller, Gotch.

3. Respiration. — Edward Smith, Haldane.

4. Glands and Secretion. — Langley, Starling, Bayliss,

Schafer (internal secretions).

5. Nerves. — Langley, Gotch, Sherrington.

6. Nerve Centres. — Hitsig, Fritsch, Ferrier Waldeyer

(neuron theory), Golgi, Ramon y Cajal, Sherrington.

7. Heart. — Gaskell, Einthoven ; Pulse — Mackenzie.

INDEX

ABSORPTION, 101

Achromatin, 40

AgRlutinins, 115

Agujari, Lucrezia, voice of, 230

Amylopsin, 98

Animal heat, 30 ; animal motion,

32

Antitoxins, 114
Arborizations, 180
Arteries, 121

Arytenoid cartilages, 227
Asphyxia, 197
Assimilation, 25
Automatic nervous mechanism,

196

Bile, 97, 139; pigments, 139;

salts, 140

Bile, circulation of, 141
Bilirubin, 139
Biliverdin, 139
Blood, 109 ; coagulation, 116 ;

corpuscles, 112; plates, 112
Botany, 12

Bowels, excretion by, 138
Brunner'a Glands, 99
Bulb, 193

Capillaries, 121, 122
Carbo-hydrates, 82
Catalytic action, 73
Cell, 38, 39
Cerebellum, 216
Cerebrum, 206

Chemistry, organic, 16 ; physio-
logical, 16

Cholesterin or cholesterol, 141
Chromatin, 40
Chromosomes, 40, 42
Chyme, 95
Circulation, 118, 120
Colloidal matter, 20, 81
Connective tissues, 56
Contractibilitv, 59
Corpora quadrigemina, 204
Corpora stricta, 205
Creatin, 134
Creatinin, 134
Cricoid cartilage, 227
Crura of cerebrum, 203
Cytoplasm, 39

Death, 28, 235

Decomposition, chemical, 67
Deglutition, 93

Dendrons, 180 ; dendrites, ISO
Development, 37
Diaphragm, 47

Digestion, 92
Dissociation, 69
Ductless glands, 150

Ear, range of, 231

Ectoderm, 46, 47

Electrical fishes, 167

Embryology, 15

Endoderm, 4ft, 47

End-organs, 176, 216

Energy, liberation of, 161 ; amount

of, 166

Enterokinase, 76

Enzymes, 70 ; classification of, 75
Epicritic, 224
Erepsin, 76, 99
Erythrocytes. 112
Evolution, 20
Excretion, 126

Fats, 73

Fecundation, 44

Fibrin, 116

Fibrinogen, 116

Food, 92

Forster, Gaspard, voice of, 231

Ganglia, 178
Gastric juice, 94
Glycogen, 147
Glycogenic function, 144
Great intestine, 99
Growth, 50

Haematoidin, 140
Haemolysins, 113
Heart, nerves of, 187
Heat, animal, 162
Hepatic vein, 103
Heredity, 45, 52
Hippuric acid, 136
Hormones, 76
Hyaloplasm, 40

Immunity, 114
Inhibition, 187
Internal secretions, 150
Intestine, digestion in, 96
Ions, 168

Karyokinesis, 45
Kidneys, 130

Lacteals, 102

Leucocytes, 59

Lieberkutin's glands, 99

Lipase, 76, 98

Living organisms, general charac-
ters of, 20, 21, 25, 26 ; chemical
composition of, 21

200

256

INDEX

Lungs, 126
Lymphatics, 110

Malpighian bodies, 131
Matter and energy, 65, 77
Medulla oblongata, 194
Mesenchyme, 48
Mesenteric glands, 101
Mesoderm, 46, 48
Motor centres, 208
Motor tracts, 190, 206
MUllerian ducts. 48
Muscle, 58

Nerve cells, granules in, 182

Nerve fibres, 170

Nerves, as conductors, 175;

effects of stimulating, 172
Nervous activities, 35
Nervous impulse, rate of, 173
Nervous system, 169
Neurones, 178
Nucleus, 39

Nutrition, complemental, 155
Opsonins, 115
Optic thalami, 205
Organ, highest tone of, 231
Ovary, 42
Ovum, 42
Oxidases, 136
Oxidation, 66

Pancreatic juice, 98

Pepsin, 76, 94

Peptones, 95

Phagocytes, 113

Philosophical questions, 239

Phones, 233

Phosgenes, 218

Physics, relations to physiology,

Physiology, comparative, 13: de-
finition of, 9

Physiological chemistry, 16

Pituitary body, 152

Placenta, 50

Plant life, 85

Pons varolii, 203

Portal system, 102 ; p. vein, 102

Proteins, 82, 105

Protopathic, 224

Protoplasm, 38; building up of,
156

Proteolytic, 76

Proximate principles, 22, 80

Ptyalin, 93

Pulmonary ventilation, 130
Pulse, 120
Purine basis, 135

Receptaculum chyli, 101

Reduction, 61

Reflex acts, 184

Rennin, 76

Respiration. 126 ; nerves of, 198

Retina, 218

Salts, 84

Sciences, relation to Physiology

12, 141
Secretion, 33
Senses, 214; classification, 216 •

delicacy of, 222

Sensory, centres, 207 ; tracts, 203
Skin, 137 ; sensitiveness of, 224
Soap, 25, 99
Somatopleure, 46, 47
Speech, 233
Spermatozoon, 42
Spinal cord, 188
Splanchnopleure, 46, 48
Spleen, 152
Steapsin, 76

Stomach, digestion in, 94
Suprarenal bodies, 151
Synapsis, 180
Synthesis, 69

Thoracic duct, 101

Thrombin, 76, 117

Thyroid, 150; cartilage, 227

Thymus, 154

Tissues, 38, 41, 51, 55, 63

Tonus of muscle. 186

Toxins, 114

Trophoblast, 46

Trypsin, 76

Urea, 16, 133
Uric acid, 134
Urine, 132

Variability, 29
Vaso-motor centres, 201
Vibrations, 130
Vocal cords, 227

Voice, 226 ; mechanism, 228 :
range of, 230 ; quality of, 232

Waste matters output, 125
Wolfflan ducts, 48

Zoology, 12
Zymogen, 72

The London and Norwich Press, Ltd., London aud No

rwich

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

AN INITIAL PINE OP 25 CENTS

WILL BE ASSESSED FOR FAILURE TO RETURN
THIS BOOK ON THE DATE DUE. THE PENALTY
WILL INCREASE TO SO CENTS ON THE FOURTH
DAY AND TO $1.OO ON THE SEVENTH DAY
OVERDUE.

BIOLOGY LIBRARY

FEB20

20Fe'6lE?

UNIVERSITY OP CALIFORNIA LIBRARY